I have some sleepers just off of the top of my head.
Gonzaga - An improving Austin Daye and a motivated Josh Heytvelt could take them to the next level. The backcourt of Pargo and Bouldin isn't too bad either. They have a lot of depth and shooting with Micah Downs and Steven Gray potentially coming off the bench.
Notre Dame - Kyle McAlarney and Luke Harangody return, as does floor general Tory Jackson. Rob Kurz is the only playing who earned significant playing time that is leaving.
Southern Cal - Taj Gibson, Davon Jefferson, and Dwight Lewis all return and averaged in double figures. Combo guard Daniel Hackett returns as well and could be a 10-5-5 guy next season. Mayo is likely gone, but some may feel Demar Derozan could be an upgrade.
Miami - Return leading scorers Jack McClinton and James Dews as well as ultra-althletic forwards Brian Asbury and Dwayne Collins. Big men Anthony King and Ray Hicks are the only contributers leaving, and incoming freshman Dequan Jones, a 6-6 wing, is one of the countries most athletic prep players. The big hole is point guard play. Either Lance Hurdle must embrace the role of distributor or rising Soph. Eddie Rios must show he is capable of playing in ACC and adjust much better the the speed and strength of the rest of the conference. If one of those two things happen, Miami could be the second best team in the ACC next season.
Illinois St. - the Redbirds finished last season on a tear and would have gained an NCAA birth if they hadn't been so brutally beaten by Creighton in the Valley Conference tourny. Osiris Eldrige averaged 16-6-2 last season and expect the rising junior to be among the leading candidates for MVC POY. Joining him on the wing is Oregon transfer Chamberlain Oguchi. Oguchi, at 6'5, is an elite athlete with a deadly outside stroke who never seemed to find any kind of consistancy in Eugene. Look for Sead Odzic, a former USC Trojan, to be more of a factor shooting the ball. ISU brings in 5 recruits, the best of which is 3star big man Jeremy Robinson.
Brigham Young - Returns top three scorers in Lee Cummard, Trent Plaisted, and Jon Tavernari. Rising Soph. Jimmer Fredette is a big time shooter and should be more of a factor behing the arc this season. Plaisted is arguably the MWC's most talented player, but Cummard is the team's most valuable. The lankly 6'7 rising senior does a little bit of everything averaging close to 16 points, over 6 boards, and 3.5 assists per. He also shot 47% from three, and 86% from the line.
Syracuse - If Donte Greene comes back they are a legit contender, IMO. But odds are he is gone. The Orange await the returns of Eric Devandorf and Andy Rautins as well as incoming wing Mookie Jones. The Cuse need rising Soph. Rick Jackson to play up to potential this season, because they are very thing inside with wide-body Arinze Onuaku the only established presence. Jonny Flynn is back as quarterback and he should flourish alongside Devandorf and do-it-all forward Paul Harris. Devendorf was off to a blistering start last season putting up 17pts and 4 dimes before a torn ACL ended his season ten games in. As far as I know Donte Greene hasn't declared, but I expect that news to come soon. If somehow he decides to stay Syracuse will be most talented team in the Big East and the most talented team they've had since Carmelo and Hakim ruled the Carrier Dome.