Tim Dierkes wrote recently at Roto Authority about relievers who could close in 2011. Dierkes is a strong writer and he makes good cases for every one of his potential closer candidates.
I suspect, though, that Dierkes' audience is mostly those who play in draft (and not auction) formats. While it's fun to try and grab the next $1 middle reliever turned closer, my advice is to avoid playing this game during the off season.
Unless you can give up a borderline freeze (or, better yet, someone you're not freezing that another owner might), here are three reasons you shouldn't chase closers-in-waiting.
1) It's a long way to next April. Johnny Venters looks great right now but the Braves could sign someone to close, Venters could blow out his arm in the spring, or the Braves might find some other internal candidate (for whatever reason). I agree with Dierkes that Venters is a logical choice for Atlanta if Billy Wagner retires, but that doesn't mean that it is the choice they will make.
2) Don't pay full price in trade for non-save stats. An argument can be made that if you trade for a solid reliever who doesn't become the closer that you're still trading for good stats. That might be true, but middle relievers - unlike closers - come out of the woodwork in 5x5. Four of the top six middle relievers in the American League (less than 10 saves) went for $1 or less, and Joaquin Benoit could have been stashed on your reserve list in April. Don't give up a valuable commodity elsewhere for the kind of pitcher you can get for free or next to nothing.
3) If you think a middle reliever is a future closer, so does your opponent. My guess is that you're in a smart league where the other 11 owners know who Matt Thornton is. It's doubtful that your opponent is going to trade Thornton to you for peanuts or because he was the best man at your wedding. You might not have to pay full closer market value for Thornton in January, but you're going to come close.
I like to speculate on future relief situations as much as the next guy, but I hate to overpay on spec. Always remember that while it's nice to get a closer off of the scrap heap for cheap, that you can do that without dropping a bundle at auction or giving up a lot in trade.