From the RacePacket email newsletter (also posted on racepacket.com):
1) Cancelled & Postponed Races
Due to the record 2010 snowstorm, the following races have been postponed or canceled:
* George Washington Birthday 10K - Feb. 13 - Canceled.
* Washington Birthday Marathon & Relay - Feb. 14 - postponed  from 2/14 to either 2/28 or 3/28
* Love the Run You're With 5K - Feb. 14 - postponed from 2/14 to 2/28
* Atholton High School 5K - canceled
* By George 5K & 10K - Feb. 13 - canceled
* TJ Indoor Track Meet #3 - Jan. 30 - rescheduled for 2/21
* MCRRC Run Aware 5K - Feb. 13 - canceled
* MCRRC Country Road Run 5 Miler - Feb. 21 - canceled
* 50+ Club Walnut Hill 5k- Feb. 21 - canceled
Due to the tragic events of Sept. 11, 2001 and the subsequent security threats, a number of races 
are being postponed or cancelled.
* SGMA Capital Challenge - Sept. 12 - Cancelled.
* Pennsylvania Avenue Mile, postponed from Sept. 15 to Sunday, Oct. 21
* Vanguard Run for Recovery 5K, postponed from September 16, to Sunday, Oct. 21
* Indian Head 210 10K, postponed from Sept. 15 to November 17
* Subaru Outback Rendezvous, September 15 - Canceled.
* Starlight Foundation, Run & Roll 5K, Sept. 15 - Canceled.
* Sri Chinmoy 2 Mile, Sept. 15 - Cancelled.
* Freddie Mac 5K, Sept. 16 - Cancelled.
* Blue & Grey Half Marathon, Sept. 16 - Postponed.
* Jones Falls Expressway 8K, Sept. 16 -  Postponed to Oct. 14.
* Air Force in Motion 5k & 10K, Sept. 29 - Canceled.
* Spectrum Challenge 10K, Sept. 29 postponed to Oct 21 at the Baltimore-Annapolis Trail.
* Mulberry Island Half Marathon & 5K, Ft. Eustis - Canceled. 
* BWI Airport 5K, Sept. 30 - changed to a 1M fun run/walk at Embassy Suites Hotel
  1300 Concourse Drive, Linthicum For directions, call 410-850-0747
* Civil War Relay, Oct. 13 - Canceled.
* Race for the Cure Ft. Monroe, Oct. 13 - Canceled.
* Army 10 Miler, Oct. 14 - Cancelled.
* Portsmouth - Semper Paratus Coast Guard 10K, Oct. 20 - Canceled.
* Dulaney High School Homecoming 5k Timonium, MD, Nov. 4 - Canceled.
* Brew to Brew race in Baltimore, Nov. 11 - Canceled
* Sri Chinmoy races in Rock Creek Park for the rest of the 2001 canceled.
* Al Lewis 10 Miler, Kensington, Nov. 17 - Canceled.
* RASAC Heritage-Greenway Trail 5 mile race, Nov. 18 - Canceled.
* Great Valley Marathon, Chambersburg, PA, Dec. 1 - Canceled.
2002
* 2002 Last Train to Boston Marathon (Aberdeen Proving Grounds)- Canceled
* Reston 10 Miler, Mar 24, 2002 - Canceled
* Clarendon 5K, April 13 - Canceled
* Governor's Bay Bridge Run, April 28 - Canceled
* Microsoft USO Defender 10 Miler - May 5 - Canceled
* Hills of Cabin John Cross Country #1 5k - Postponed to Saturday, May 11
* Men's Season 5K, Oct 12 - Postponed to Saturday, Oct. 19, 2002
* Run For Kathy 5K, Oct 12 - Postponed to Saturday, Nov. 16, 2002
* Rockville 5k & 10K, Oct 13 - Postponed to Dec. 9, 2002
* Mental Health 5K, Oct 12 - Postponed or possibly canceled.
* Help the Homeless Community Walk in Reston, Oct. 19 - canceled
* Help the Homeless Community Walk in College Park, Oct. 20 cancelled.
* Goblin Gallop 5K, Oct 27 - postoponed until spring.
* YWCA 5K in Baltimore, Nov. 9 - canceled
2003
* GW Birthday 10K Classic, Feb. 15 - canceled due to snow.
* Washington Birthday Marathon & Relay, Feb. 16 - canceled due to snow.
* By George 5K, Feb 22  - canceled due to snow.
* Columbia 10 Mile Challenge, Feb 23  - canceled due to snow.
* Potomac 4k/8K/12K, Mar 1 - canceled due to snow.
* B&A Trail Marathon, Mar 2 - canceled due to snow.
* MCRRC Carderock Tow Path Run 15K, Mar. 8 - canceled due to snow.
* DC Marathon, Mar 23 - canceled due to Iraqi
* Ocean City Half Marathon, April 6
* Frederick Women's Distance Festival, Sept 20 - canceled by police.
* City of Pittsburgh Great Race 5k & 10K, Sept 28 - canceled due to budget cuts.
* DCRRC Bread Run, Dec. 14 - canceled due to ice storm.
* MCRRC Jingle Bell Jog, Dec. 14 - canceled due to ice storm.'
2009
* Columbia Metric Marathon, Dec. 6 - canceled due to ice
* LifeTime Fitness Reindeer Run 5K, Dec. 19 - canceled due to snow
* PVTC Christmas Caper 5k & 10K, Dec. 19 - canceled due to snow
* MADD Red Ribbon Run 5K, Dec. 31 - canceled