I was unaware that Railfan & Railroad magazine has a contest. Unfortunately entry deadline is extremely soon, last day of September or first day of October, something like that. $200 first prize; don't recall the theme, if any. Sorry for not having more info; I couldn't find any info online. Now I know to look for it next year.
Trains magazine also has a contest (link here, big file, 3.6MB), first prize is a Canon 50D! The theme: "Bridging the Gap." Deadline October 31; for details follow the link.
Finally, the Center for Rail Photography and Art is doing their annual contest again. This year's theme is "Beyond the Locomotive" with the added explanation that "This year’s theme challenges the photographer to understate (or even eliminate) the locomotive in the photograph and emphasize other aspects of the railroad environment." First prize is also a Canon 50D! Deadline December 31; modest entry fee of $10 for non-members of the Center. Link here.
Good luck, everyone!
PS: I forgot all about Day In North America, a competition/compilation where everyone submits their shots taken on one day; the selected shots appear in an issue of Railroads Illustrated. That day was October 3, 2009, so it is too late to make a plan, but if you took a nice shot that day, the information for submission can be found here.