mlb 09/02/08 2:35 PM ET Jonathan Mayo is a senior reporter for MLB.com.]]> Some will get serious playing time, others will simply get the experience of seeing what it's like to prepare for the game at its highest level on a daily basis.

For fantasy owners, this time of year provides the opportunity to give your roster a late boost, or to scout out options for keeper leagues. With that in mind, here's a list of the best the September callups have to offer, with a focus on players in the bigs for the first time:

1. Travis Snider, OF, Blue Jays: Snider was a surprise callup -- he wasn't on Toronto's 40-man roster -- but he might help out with nice numbers down the stretch. The 2006 first-rounder has already received seven at-bats, so it's clear the Jays intend to see what he can do. Snider can hit for average and power, and while he might be a little up and down at age 20, he makes quick adjustments and could drive in a few runs this month. At the very least, anyone in keeper formats will want to jump on a guy with a .299 average and a .513 slugging percentage since signing out of high school in 2006.

2. Aaron Cunningham, OF, Athletics: Cunningham also wasn't on his team's 40-man roster, but it helps that he's in his protection year. And what a year it's been for the outfielder, who hit a combined .329 with 17 homers and 15 stolen bases at Double-A and Triple-A. He should get fairly consistent playing time, especially with Frank Thomas out with a quad injury, but owners shouldn't expect miracles here. Just 22, Cunningham may not do more than steal a few bases. That said, AL-only owners may want to consider taking a shot.

3. Matt Antonelli, 2B, Padres: If you look at his season statistics (.215 AVG, .657 OPS), you might wonder why Antonelli got the call. But the 23-year-old finally started coming around in August, hitting .290 with an .864 OPS for the month. I know, not earth-shattering, but much closer to the numbers he posted in his impressive '07 season (.307 AVG, .895 OPS). He's going to get a long look in San Diego, so if you need a middle infielder, it's worth taking a risk in NL-only leagues. I still believe in the guy, and it's not just because I've got him in my sim league.

4. Wade LeBlanc, LHP, Padres: Again, the season numbers aren't pretty (5.32 ERA), but you need to dig a little deeper. The 2006 second-rounder struck out more than a batter per inning, and he posted a 2.86 ERA with a .191 batting average against in seven starts after the All-Star break. His August ERA was a solid 3.55, and it would have been an outstanding 1.67 if you threw out one awful six-inning, eight-run outing. LeBlanc is scheduled to start Wednesday in Los Angeles; I might take a flier on him in an NL-only league right now.

5. Jon Niese, LHP, Mets: This one is more for next year than this one, but the 21-year-old southpaw possesses legit stuff and could be a good mid-rotation choice in the future. The Mets will throw him right into the fire with a start vs. the hard-hitting Brewers on Tuesday.

6. Kila Ka'aihue, 1B, Royals: I'm not sure how much he's going play in K.C., but he at least warrants a mention on this list. Ka'aihue, whose brother is in the Braves organization, was a 15th-rounder back in 2002. He's always shown some power (21 HR in '07) but didn't put it all together until this year, when he batted .314 with 37 homers, 100 RBIs and 104 walks in 124 games across two levels. Those in AL-only leagues will want to watch carefully to see if he gets some time at first. Even if he doesn't hit for average, Ka'aihue might deliver some homers and RBIs right away.

7. Greg Golson, OF, Phillies: At this point, we're getting into the guys who are mainly for keeper consideration. Don't expect Golson to do much of anything in September except make the occasional pinch-run or defensive-replacement appearance. He could wind up with a few steals, but likely not enough to warrant an active roster spot. That said, Golson has begun to figure things out on the baseball field, and he finished this year with 13 homers and 23 steals. It might take a while before he reaches his full potential, but stashing him on your reserve list and watching him develop could be a lot of fun.

8. James McDonald, RHP, Dodgers: This guy is a real sleeper pick for me. A year ago, he struck out 168 and walked just 37 in 134 2/3 innings across two levels. He followed that up by posting a 3.26 ERA and a 141/53 K/BB ratio in 141 combined innings at Double-A and Triple-A this year. McDonald isn't likely to make much of an impact this month, but his performance could serve as a springboard for a rotation spot in '09. Keeper-league owners should consider making room for this guy.

9. Fernando Perez, OF, Rays: As with Golson, chances are Perez will be limited to pinch-running and defensive-replacement duties. That said, it's worth noting anytime a guy gets called up after stealing 43 bases in Triple-A. Perez strikes out too much, but he also draws enough walks to make use of his speed. It's unclear how the 25-year-old fits into the Rays' long-term plans, but even if he winds up as the team's fourth outfielder, he has the speed to help out AL-only owners.

10. Lou Marson, C, Phillies: Marson, who set professional highs in average, on-base percentage and slugging percentage in his first taste of Double-A, was rewarded with a callup after playing in the Olympics. He'll be Philly's third catcher for now, but with all due respect to Carlos Ruiz and Chris Coste, the 22-year-old is the team's catcher of the future. It may not be a bad idea to grab him and stash him away on your reserve list.

I'll be back next week with more callup news, as not every top prospect is in the bigs yet (I'm talking about you, Dexter Fowler). Stay tuned ...

]]> http://mlb.mlb.com/mlb/fantasy/index.jsp /milb/stats/stats.jsp?n=Travis Snider&pos=OF&sid=milb&t=p_pbp&pid=501983 http://shop.mlb.com/shop/index.jsp?categoryId=1998124