Upcoming return airdates  for shows that took an Olympic break or are premiering a new season. (via SFTV.org):

Flash Forward (ABC)                   Mar 18  (Season 1 Resumes)
The Clone Wars (Cartoon)              Mar 19  (Season 2 Resumes)*
Supernatural (CW)                     Mar 25  (Season 5 Resumes)*
Vampire Diaries (CW)                  Mar 25  (Season 1 Resumes)*
V (ABC)                               Mar 30  (Season 1 Resumes)
Doctor Who (BBC)                      Apr  3? (Series 5 UK Debut)
Doctor Who (BBC America)              Apr 17  (Series 5 US Debut)
Fringe (FOX)                          Apr  1  (Season 2 Resumes)
Merlin (SyFy)                         Apr  2  (Series 2 US Debut)
Stargate Universe (SyFy)              Apr  2  (Season 1 Resumes)
Smallville (CW)                       Apr  2  (Season 9 Resumes)*
Going Postal (Sky One)                Apr 3/4? (Miniseries UK Debut)
Riverworld (Syfy)                     Apr 18  (Miniseries Debut)

*Not found on sftv.org.