To me it would be someone like Andrew Bogut or Greg Oden. A big man who has underperformed (read: been injured or in bad conditions) so far, who would grow immensely on a team where defense is preached, and with a point guard like Rondo.
I'd put someone like Josh Smith on the list of players I'd like the least to see with Rondo (Hence, see in green). Unlike Rondo, who's probably equally as bad a shooter, this guy does not strike me as an intelligent player (on offense). His shot selection is horrendous, and on a team where the point guard can't shoot, everyone else should be able to. Smith may shoot a lot, but from what I've seen, his shot is definitely a weakness.