If you're on a limited budget and using a PC at all, you might consider (don't laugh) a Sound Blaster Live or Audigy (you should be able to get a Live for $50 or maybe even less). A lot of folks don't quite understand but the built-in Soundfont 2 technology (when combined with their freebie Soundfont editor Vienna) allows you to do moderately sophisticated sample editing, multi-sample layering, and wavetable bank building. (There are other non-SB soundcards out there with Soundfont compatability, as well.)
I'm not completely familiar with all the particulars of each model but the SB Live Value (basically the cheapest of the cheap) uses PC host system RAM (I have no ideas how or how well the SB Live for Mac works, sorry) to store the samples. With today's rock bottom system RAM prices (around here you can pretty much get 256 MB for $50 or less) that means you can probably devote anywhere from 32 to 256 or more megs of RAM to samples -- obviously a huge amount by keyboard sampler standards. And the Vienna editor is as well suited to creating drum/percussion and sound effects kits as it is to multi-samples.
In fact, I just spent an hour or so last night grabbing free Soundfont samples off the Creative Labs and Sonic Implant sites -- as well as a few others. The best scores were a bunch of really decent drum kits. If you know how crummy the basic drum kit samples sound in the SB you'll be amazed to find out what's out there for free. (And, of course, folks like Sonic Implants will be all too happy to sell you some of their sample sets for, well, typical sample set prices. Although they also sell small subsets of hits and loops in downloadable form for as little as $10 a subset.)
Even if you already have a 'pro' soundcard, you can still slap a SB in your machine (they can coexist nicely) to use for its Soundfont, MIDI i/o, game compabability, etc.
Another software answer for the PC (it will still require a soundcard of some kind of course) is the Gigasampler. I haven't used it but its generating a log of favorable comment and seems to have considerable momentum. (Another place where falling system RAM prices have opened a window of opportunity.)