The Whirlwind IMP-2 direct box is a simple, inexpensive unit that is popular, has been around for a long time and does the job just fine ...
http://www.musiciansfriend.com/pro-audio/whirlwind-imp-2-standard-direct-box
You can spend a lot of money on boutique direct boxes if you choose to * but (IMHO) it's primarily the sound technician's taste in sound and chops with the equipment at hand that is going to make it or break it for the quality of your FOH bass sound. A number of years ago, I played the Columbia Pike Blues Festival where they supplied the backline including a GK 800RB head along with EV 2x10 and 1x15 cabinets for the bass. Despite the GK 800RB having it's own DI, they chose to use an ultra cheap Horizon passive direct box (that I'd seen in stores for like $20) right off of my Fender Precision. A local cable access TV channel filmed the show and I got the contact number of the guy heading up the film crew so that I could get a copy of it later. Anyway, I got a dub directly from the original film source onto a good quality VHS HI-FI tape and it was the absolute best tone I ever heard of myself, despite the bare bones DI right off my bass. The mix of the entire performance was first rate, too ... the sound guy definitely knew what he was doing.
* And it doesn't take all that long into spending big bucks on a DI that you get into the "splitting hairs" realm. If you really want to go "Rolls Royce" without getting into silly money, the Countryman Type 85 direct box is a VERY well regarded unit ...
http://www.sweetwater.com/store/detail/DT85/