Computer based drum machine to play drum loops?

I just got a new Roland RD300GX piano and I'd like to play it in a piano bar setting. Unfortunately, although it's a great keyboard, the built-in drums are as lame as can be.
So I've created a bunch of drum loops: some 1-bar intros, 4-bar phrases, and some endings, in various styles. Now I'd like to use my computer as a drum machine so I can play the drum tracks via midi along with my keyboard.

I'm envisioning of some kind of app that would allow me to select my "style" set and a tempo. Then I could tap "Z" to start playing the intro, "X" for the phrase variation 1, "C" for variation 2, "V" for an ending, etc. Each selection would wait until the previously selected loop was done. If I didn't select anything, the loop would repeat indefinitely.

Does anything exist like this now? If not, can Sonar LE be used to do it (outside of creating the loops to begin with)? Any other ideas on how to play the loops?

Hey, thanks for the quick reply and the welcom, Bitflipper!
I'll check out Jamstix as a possibility. My old keyboard was a Korg i3 which was an "intelligent arranger". This meant that it had tons of drum tracks in a variety of styles and you could pick them easily while performing (it also watched your chord patterns and supplied backup instrumentation like guitars, horns, etc. too). The old Korg died, but I at least need to get a good drum backing to my impromptu tunes (usually requests, so I need to pick a drum groove quickly). Interestingly, I've been a professional drummer for 40 years (played lots of studio work and at the White House), just recently going over to the melodic side. I'm so embarassed by the crap that is put out as midi drums (and built-in drum tracks in keyboards). I'm satisfying my melodic needs now, but the drums sure are a sore subject now.

Anyone else have any suggestions?