The popular options at third are currently Garrett Atkins, Ty Wigginton both acting as placeholders for Joshua Bell. Most people have pretty much decided that the best action would be to use Atkins as the starting third baseman with Wiggy or Justin Turner as backup until Josh Bell comes up midseason where then Atkins can be traded or released as seen fit.
Now that is a pretty good plan depending on whether Atkins can provide value at third. Josh Bell had a dominating year last year at Double-A in both the Dodgers and the Orioles systems. His wOBA (This is a players offensive value translated into OBP numbers so a wOBA of .340 should be around average) was higher than .390 at both stops. The year before was still very good at .368. That's one year of being pretty good and one year of dominating double-A the first time he's been there. Granted that's built on good BABIP's but with the exception of a short 20-game stint at Advanced A, Bell has posted BABIP's over .320 every year suggesting that he has good speed. Bell is a very good prospect. He will probably regress somewhat next year as he backs down from his dominating season, but he should still be above-average as his lowest wRC+ (same as with OPS+ anying above 100 is good, below is bad. For the minor leagues the stat is adjusted for the league averages but is NOT park neutral) is 119 in 2008. To be above-average in one's worst year says something about a player.
Atkins the past two years has gone downhill. Matt Klaass wrote an article detailing his downward spiral. Part of the reason for his terrible last year lies in his career-worst BABIP of .247 more than 60 points lower than his second-worse BABIP. It's likely that he could revert to at least being playable. More worrying is his sudden drop in power with his ISO dropping to .119 while playing at Coors. Without his power Atkins loses much of his value.
Wiggy is set to play a backup role to both corners or possibly perform some sort of platoon at first. Last year was his first below-average offensive contribution since 2004. Wiggy had a down year losing power and OBP. I'm somewhat confused by his dramatically lower OBP since he had a higher walk to strikeout ration than when he played for the Devil Rays. I guess the 8 point difference in BABIP accounts for the rest although the math seems odd. Anyway he could be a candidate to rebound like Atkins, but since there are no easy things to point to as the cause for his fall besides losing his power I'm not nearly as expectant as I was with Atkins. However he did have the better year the year before, which switching leagues should not have changed. wRC+ which neutralises ballpark factors for major league ballparks had Wiggy at 128 in 2008 and then just 88 in 2009. Part of this may be the change to the harder league along with maybe some natural aging as Wiggy will be 32 this year. Part of it may be adjusting to being more of a bench player. I'm not really sure what happened with Wiggy but he should rebound to some extent this coming year.
Now onto the forgotten or surprise candidates. Justin Turner and Scott Moore will primarily be working to become backups. However a key injury or a good spring training could move them forward on the depth chart.
Scott Moore is the forgotten child of all the third base candidates. He actually made the team out of spring training in either 2008 or 2009 (I believe 2009 but somebody can correct me if I'm wrong) only to go down with an injury. He ended up playing only 32 games last year. In 2008 he played 82. So basically the past two years he's been dealing with injuries. However the past three years he has posted a wRC+ in triple-A of 100 or better. He posted a wRC+ of 125 while playing for the Cubs affiliate in 2007. In 2008 and 2009 while playing for Norfolk, a pitcher's park, (remember that wRC+ in the minor leagues does not yet adjust for park factors) he posted a wRC+ of 100 and 119 respectively. The 2008 and 2009 numbers should really be combined to produce a better sample size, it means that in a pitcher's park Scott Moore was a slightly above-average hitter. More than that Scott Moore has power (7 homeruns in 32 games while playing some of his games in pitcher's parks) and would presumably be a better fielder than Wiggy and Atkins.
Justin Turner is currently being acknowledged as a possible utility candidate to challenge Andino. He apparently plays both third and second so he might be the best defensively. He was one of the fringe prospects to be picked up in the trade with the reds. He doesn't seem to have much power but he does post a very good OBP. In fact in his 12 game stint with the Orioles last year he managed to walk more than he struck out. While unlikely to happen in larger samples it does speak to the good plate dicipline that he has developed. Unfotunately most high OBP minor leagues with little power have trouble in the majors. With little power to punish many pitchers pound the strikezone against them. The good news is that Justin Turner posted an above average wRC+ at Norfolk similar to Scott Moore. He also has the chance to make the team as an utility candidate unlike the other options at third