This calendar is definitely a work in progress and focuses on events I have some interest in - it is not meant to be a comprehensive list for the northeastern US (or anywhere else, for that matter!) As always, check with the event organizers for the most up-to-date info.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
January
DAR Moose Run 5mi snowshoe race 1-2-11 postponed
Turner Trail 5mi snowshoe race 1-8-11
Frozen Assets 5k snowshoe race 1-8-11
Bear Paw Classic 5-8k snowshoe race 1-8-11 postponed
Olde Salem Greens 3mi snowshoe race 1-8-11
MHRRC Recover From the Holidays 50k run 1-8-11
Watchung Winter Trail Marathon/50k 1-8-11
Dirt Dawg 8mi trail race 1-8-11
Resolution Run 10k trail race 1-8-11
Weston Winter Duathlon 1-9-11
Greylock Glen 4mi snowshoe race 1-15-11
Feel Good Farm 8k snowshoe race 1-15-11
Winter Wild Whaleback Mtn 2.5mi race 1-15-11
Brave the Blizzard 3mi snowshoe race 1-16-11
Mendon Winterfest 5k & 10k snowshoe races 1-16-11
Frontenac Park 7.3k snowshoe race 1-16-11
Chilly Cheeks 7.25mi trail race 1-16-11
Run for Regis 50k trail race 1-16-11
Hoot Toot and Whistle 3mi snowshoe race 1-22-11
Winona Forest Winterfest 3.8mi snowshoe race 1-22-11
Whitaker Woods 4mi snowshoe race 1-22-11
Highland Forest 5k snowshoe race 1-22-11
Tubbs Romp to Stomp NJ 3k snowshoe race 1-22-11
Constitution Hill 3mi snowshoe race 1-23-11
Lake Effect 2,4, & 13mi snowshoe races 1-23-11
Dewey Challenge the Mountain 5/10k snowshoe races 1-23-11
Bradbury Squall 3.5mi snowshoe race 1-23-11
Darts Lake Dash 5k snowshoe race 1-29-11
Sidehiller 4mi snowshoe race 1-29-11
Tubbs Romp to Stomp VT 3k snowshoe race 1-29-11
Curlys Record Run 4mi snowshoe race 1-30-11
Darts lake Dash 10k snowshoe race 1-30-11
Medved Winter Challenge 5k snowshoe race 1-30-11
February
Northfield Mountain 3.8mi Snowshoe Race 2-6-10
Exeter Snowshoe Hullaballoo 4mi 2-6-10
MA Winter Triathlon 2-6-10
Saratoga Winterfest 5k Snowshoe Race 2-7-10
Northern VT 8k Snowshoe Challenge 2-7-10
Beaver Lake Midwinter Blues 5k 2-7-10
Camp Saratoga 8k Snowshoe Race 2-13-10
Horse Hill 7k Snowshoe Race 2-13-10
Frosty's Dash for a Cure 5k Snowshoe Race 2-14-10
Kingman Farms Moonlight 5k Snowshoe Race 2-20-10
Hallockville 4mi Snowshoe Race 2-20-10
Covered Bridge 4mi & Half Marathon Snowshoe Races 2-21-10
King Pine Winter Triathlon 2-21-10
Moody Spring 5mi Snowshoe Race 2-27-10
Joppa Hill 2.5k/5k Snowshoe Races 2-27-10
Saratoga Martial Arts Festival 2-27/28-10
Ugly Mudder 7.25mi trail run 2-28-10
March
USSA National Snowshoe Championships 10k/Citizens 5k 3-6-10
Hawley Kiln Notch 5mi Snowshoe Race 3-7-10
Pineland Farms Winter Triathlon 3-7-09
Northeast Paddlesports & Outdoor Expo ?
Pittsfield Snowshoe Half Marathon/Marathon ?
Celebrate Life Half Marathon ?
MA State Championship Snowshoe Race 3-13-10
Granite State Snowshoe Championships 3-14-10
New Bedford Half Marathon ?
Catamount Sunset Snowshoe Race 3-20-10
Big Island International Marathon 3-21-10
Run the Reservoir 15k ?
Wurtsboro Mountain 30k road race ?
Odd Man Mountain Bike Duathlon ?
The Fells Trail Races ?
Mudders & Grunters 5mi trail race ?
Eastern States 20mi Road Race ?
Whidbey Island Marathon ?
April
Spring Forward Distance Run 15k 4-5-09
Bimbler's Bash 10k trail run 4-5-09
Great Bay Half Marathon 4-5-09
Northern Nipmuck 16mi trail race 4-11-09
Merrimack River 10mi trail race 4-11-09
Muddy Sneaker 20k trail race 4-18-09
Dodge the Deer 5k trail run 4-19-09
National Duathlon Festival - off road races 4-25-09
St John's/St Ann's Spring Runoff 10k 4-25-09
Delaware Trail Marathon & Triple Crown Trail Races 4-25-09
Adirondack Sports & Fitness Summer Expo 4-25 & 4-26-09
Muddy Moose 14mi trail race 4-26-09
National Duathlon Festival - on road races 4-26-09
Leatherman's Loop 10k trail race 4-26-09
George Wodicka Hook Mountain Half Marathon 4-26-09
Big Sur International Marathon 4-26-09
Highland Park 7mi Trail Race 4-26-09
Wild Indian Duathlon 4-26-09
Blue Hills 10mi trail race 4-26-09
May
Cumberland Duathlon 5-2-09
Medved Madness 15mi trail race 5-3-09
Seven Sisters 12mi Trail Race 5-3-09
Platte Clove Mountain Run 3mi 5-6-09
Thom Bugliosi 26k trail run 5-9-09
Salmon 5.5mi River Run 5-9-09
Mt. Tom Road to the Pogue 6.1Mi Trail Race 5-9-09
Block Island Shad Bloom 10k trail race 5-9-09
Morfun Wapack trail races 5-9-09
Rochester Spring Classic Duathlon 5-16-09
Ottawa Early Bird Duathlon 5-16-09
West Point 5k/10k 5-16-09
Soapstone Mountain 14.5mi trail race 5-17-09
Olana Star Loop 10k trail run 5-20-09
Highland Forest 10-20-30mi trail runs 5-23-09
RecWay 10k 5-23-09
Pineland Farms Trail Challenge 25k/50k/50mi 5-24-09
Twilight 7.4mi Trail Race 5-29-09
June
High Rock 2.25mi trail run 6-3-09
Powerbar Yellowjacket 4.5/9mi Trail Races 6-6-09
Tortoise & Hare 10k Trail Run 6-6-09
Nipmuck Trail Marathon 6-7-09
Northfield Mountain 10.3k Trail Race 6-13-09
Greylock 13.5mi Trail Race 6-21-09
Tanglefoot 5/10mi Trail Runs 6-21-09
Summer Solstice 14k Trail Race 6-24-09
Forge the Gorgeous 7mi Trail Race 6-25-09
There's A Black Fly In My Eye 15k Trail Race 6-27-09
Rochester Harborfest 10k 6-28-09
Adirondack Distance Run 10mi road race 6-29-09
Cranmore Hill Climb 11k 6-28-09
July
Finger Lakes Fifties trail races 7-4-09
Overcliff/Undercliff 4.7mi trail race 7-6-09
Moonlight in Vermont 4mi road race 7-11-09
Forest Frolic 8k/15k trail races 7-12-09
Bradbury Scuffle 6mi trail race 7-12-09
Skyline 7.2mi trail race 7-12-09
Lou's Run 4mi trail race 7-13-09
Super Summer Seminars 7-18 & 7-19-09
Bear Creek 21k trail race 7-19-09
Patterson's Pellet 3mi trail race 7-20-09
Erie New Times Presque Isle Duathlon 7-26-09
Blueberry Run 4mi trail race 7-27-09
August
Peoples Forest 7mi trail race 7-31-10
Race the Train 8.4mi road race 8-7-10
Indian Ladder 15k trail race 8-15-10
New Paltz Summer XC series awards 8-3-09
The Dam 10.5mi trail race 8-7-10
Chingachgook Challenge Half Marathon 8-7-10
Dennings Point 5k trail race 8-8-09
Rosendale Plains 4.4mi road race 8-8-09
'Dam' Good Trail Run 20k 8-22-10
Savoy Mountain 11/22mi trail race 8-15-10
Bradbury Mountain Breaker 9mi trail race 8-16-09
Mountain Madness Runs 8-16-09
Mt Toby 14mi trail race 8-22-10
Green Lakes Endurance Runs 50/100k 8-29-10
Race to the Top of Vermont 4.3mi mountain race 8-29-10
September
Oak Tree Half Marathon 9-5-10
Wapack 17.5mi trail race 9-5-10
Monster Marathon/Half Marathon 9-5-10
Mt Greylock 8mi road race 9-6-10
New Haven 20k road race 9-6-10
Maple Leaf Half Marathon 9-11-10
Liverpool ARC Half Marathon 9-11-10
Run Around the Block 15k road race 9-12-09
Red Apple 5k/10k trail races 9-11-10
Schenectady County Pedal-Paddle-Run 9-11-10
Curly's Trail Marathon/Half Marathon 9-12-10
New England Martial Arts Camp 9-12-09
Pisgah Mountain 23/50k trail races 9-19-10
Rochester Marathon/Half Marathon 9-12-10
Josh Billings RunAground Triathlon 9-12-10
SOS Triathlon 9-13-09
Bradbury Bruiser 12mi trail race 9-13-09
Erie Marathon 9-13-09
Jordan Alpine Classic 8.5mi run cancelled for 2010
MDI Half Marathon 9-19-09
Adirondack Marathon/Half Marathon 9-20-09
East Rock Challenge 5mi road race 9-20-09
The Dam Half/Full Trail Marathon 9-20-09
Greenport 5k trail run 9-25-10
Pfalz Point 10mi Trail Challenge 9-26-10
October
Chinese Martial Arts Expo New England 10-3-09
Rochester Autumn Classic Duathlon 10-4-09
Rochester Autumn Classic 4.5/9mi trail race 10-4-09
Breakneck 20k trail race 10-4-09
Pinnacle Challenge Double Duathlon 10-4-09
Treetops to Rooftops 5k 10-4-09
Houghton's Pond 6mi trail race 10-4-09
Monroe Dunbar Brook 10.5mi trail race 10-11-09
Danby Down & Dirty 10/20k trail runs 10-11-09
Bizz Johnson Trail Marathon 10-11-09
Greylock Ramble 10-12-09
Green Mountain Marathon 10-17-09
Black Diamond Offroad Duathlon 10-17-09
An Afternoon with the Masters 10-17-09
Ontario Pathways Great Pumpkin Walk 10-17-09
Ridgewalk & Run 15mi trail race 10-18-09
Mohawk Towpath Duathlon 10-18-09
Jensen Stables Ultimate XC Challenge 10-18-09
Billy Goat 5k trail run 10-18-09
CT Martial Arts Festival 10-24 & 10-25-09
Hairy Gorilla Half Marathon 10-25-09
Niagara Falls International Marathon 10-25-09
Groton Forest 9.5mi trail race 10-25-09
November
After the Leaves Have Fallen 20k trail run 11-1-09
Fall Back 5mi Trail Race 11-1-09
Busa Bushwhack 5/10mi Trail Race 11-1-09
Mendon Trail Runs 5/10/20/50k 11-7-09
Renaissance Martial Arts Festival 11-7 & 11-8-09
Bobcat Trail Marathon 11-8-09
Stone Cat Ale Trail Marathon/50mi 11-8-09
Dirt Cheap Stage Race 11-14 & 11-15-09
Taconic Trails Runs 5k/10k 11-15-09
Adirondack Sports & Fitness Winter Expo 11-21-09
Lil' Rhody Runaround 8.5mi trail race 11-22-09
RT Turkey Run 5mi 11-28-09
December
Gail's Trail Run 10k 12-6-09
Last Chance Trail Run & Pancake Breakfast 12-12-09
It's A Wonderful Run 5k 12-12-09
Snow Cheap Snowshoe/Trail Race #1 12-16-09
Albany Last Run 5k 12-19-09
I Love Woodford 5k Snowshoe Race 12-27-09