What's left on Mike Rizzo's offseason to-do list?

It's less than a month until pitchers and catchers report to Nationals spring training at Space Coast Stadium in Viera, Fla., but don't expect general manager Mike Rizzo to be any less diligent about adding to his roster or looking for creative ways to improve his ballclub between now and Feb. 19. "We're trying to improve ourselves in the rotation and in the bullpen and any other way we can, and we're certainly open-minded and we'll not stop working," Rizzo said Wednesday. "We're still trying to turn over every rock to get things done." Thursday's announcement that the Nationals had agreed to a one-year deal with reliever Brad Lidge to serve as a set-up man and bullpen sage is an example of the kind of late-in-the-offseason move that can pay big dividends. The $1 million LIdge will earn makes him a low-risk, high-ceiling signing, a small move that can have a larger-than-expected impact. So what's left on Rizzo's offseason shopping list? * Despite publicly endorsing Jayson Werth's ability to man the position, Rizzo continues to search for a center fielder. Maybe B.J. Upton and/or Michael Bourn won't be available until they reach free agency after 2012, but Rizzo could sign someone or work a trade for a short-term fix, someone who could handle center field on a regular basis this season and shift into a fourth outfielder role for 2013 (assuming they remain on the roster). A GM's favorite time to do something unexpected is when no one is prepared for it, so it wouldn't be surprising to see Rizzo pull off this kind of an under-the-radar move. * If Werth plays center and the Nationals decide that Bryce Harper isn't ready for the majors, who plays right field? The Nationals could always put Werth back in right and use a Mike Cameron-Roger Bernadina hybrid. Or they could use Werth in center and make do with a Cameron/Bernadina platoon in right (until Harper is ready to take over there, which shifts Werth back to center). Or Rizzo could make a run at a free agent to beef up his platoon options at either position, though he'd probably be more comfortable with Werth in center. Once spring training is under way and teams start making cuts, he'll be scouring the waiver wire to see if there's someone who makes sense. Cameron could have one more season left in him; we'll see. The Nationals aren't sold on Bernadina, who hasn't seized opportunities when they've been presented in the past, so he may be running out of chances. * While Rizzo has heeded manager Davey Johnson's pleas for a beefed-up bench - with the addition of guys like Mark DeRosa and non-roster invitees Cameron and Xavier Paul - expect the search for reserve punch to continue through spring training and into the regular season. Basically, Rizzo and Johnson will watch the waiver wire and see if anyone available is better than what the Nationals already have. Watch where DeRosa plays in Grapefruit League - if DeRosa spends most of his time at second, third and corner outfield spots, expect the Nationals to be on the lookout for a right-handed-hitting first baseman/pinch hitter to fill the void created by Chris Marrero's hamstring injury. If DeRosa plays a lot of first base, they might be looking for a spare infielder. * The Nationals look to have a potentially strong pitching staff, but does any team really ever have enough pitching? Nobody goes a whole season with only five starting pitchers - and then there's the issue of how long Stephen Strasburg will pitch before maxing out his innings limit in his first full season after Tommy John surgery. Craig Stammen is reliable, but Yunesky Maya hasn't exactly shown he's a viable insurance policy. Without guys like Tommy Milone and Brad Peacock knocking at the door, the Nats could be in the market to pick up a fringe major leaguer who could be stashed at Triple-A just in case. In the bullpen, Johnson could have a pair of lefty long relievers (Tom Gorzelany and the loser of the rotation competition between John Lannan and Ross Detwiler), though he'd prefer a traditional lefty/righty long tandem. If the Nats add to the relief corps, a right-hander who can work multiple innings might make sense. Rizzo won't be Dumpster diving as much as he'll be focusing a critical eye to other teams' castoffs, guys who are out of options, pushed off the depth chart because of a trade or who have had their position taken by a top prospect. Every team faces tough roster decisions in spring training; Rizzo's challenge is seeing if any of the guys who will become available make the Nationals a better team.