Baseball America raises some interesting possibilities in their Rule 5 preview. It's in the subscribers' area and I don't want to get Charlie in trouble by copying from there, but some guys who struck me as maybe worth a shot:
LH relievers: Pedro Figueroa (A's) and Jose Lugo (Twins), both hard throwers. Lugo has a high K rate and is also a strong groundball pitcher.
RH starter: Matt Torra (D'backs), former 1st rounder who had shoulder surgery. Sinker/slider guy who looks like a 4th/5th starter/innings eater. (Yeah, OK, we're loaded with those.)
RH relievers: Morlan, of course. Also Dodgers' Javy Guerra (96 mph) and Cards' Luis Perdomo (nasty slider, RH batters hit .153 against him in 2008).
One interesting hitter: 3B Jesus Guzman. He's 24 and has bounced around, but had a breakout 2008 season, hitting 364/419/500 in the Texas League and following it up with a monster winter so far in Venezuela. He just signed with the Giants as a minor league FA.