The projections for the 2015 draft are starting and here is Chad Ford's list:
KU is the only school with 2 top 10 and 3 top 20 picks. Of course this is very premature as more guys from Kentucky (Harrison twins) and maybe Duke will likely also go.
Here is another one from NBA Draft
2 top 5, 3 top 10 and 4 top 30 picks.
Looking at several mock drafts, Alexander and Oubre are generally rated top 10 and in many top 5. Selden is generally top 15 and I have seen him as high as 5. All three are potential lottery picks. Ellis is generally ranked as late first round or early second round, but a good showing in the upcoming season could up raise his standing into a borderline lottery pick.