Bass POD. Great compressor, overdrive effects, easy to use. The SVT, Eden, Gallien-Kruger, and Acoustic 360 emulations are excellent- there are 15 amp models and one preamp model. Some of the effects are good like the octave, phase shifter, and Big Muff distortion. $350. The Bass POD is one of the best investments I've ever made in my studio.
SansAmp Bass DI. $180. It's highly regarded for a DI device. They also have a version called the Bass RBI that is in rackmount form and it has more EQ control, $300.