Their most glaring needs are at shooting guard and backup center. This year's draft has numerous players who could fill such a void nicely.
If they go the 2-guard route, they'll almost surely look for a wing who has some range on his jump shot. The Bulls ranked second to last in the league during 2012-13 in three-point field goals made per game (5.4). They could clearly use some help in this arena.
A backup center is another valid option to pursue. Since the departure of Omer Asik last summer, the Bulls have been limited in their frontcourt depth. Veteran Nazr Mohammed was barely serviceable, and it's evident that an upgrade is necessary.
So, which route will the Bulls go with the 20th pick in Thursday's draft? Assuming they don't make a blockbuster trade (interestingly, according to ESPN's Marc Stein, there are rumors about the Bulls trading Luol Deng for a high selection), these draft targets make perfect sense for the Bulls going forward.