Don't forget that the size of the internal buffer is equally as important as frame per sec. Nothing is more fustrating than missing some great shots because the camera's internal buffer fills up too fast. Once that internal buffer is filled, you'll only be able to shoot as quick as the camera can offload to the media card. Don't worry about 8+ MP.
The nikon D50 (i'm assuming D-50 shoots with one) shoots 2.5fps but only sustainable until its internal buffer of 12 JPG images are filled. The D80 is 3fps up to 23 jpeg images. The D40 is rated at 2.5fps and listed as "unlimited" jpg for buffer. I'm assuming this means that the write to the media card is fast enough to keep up with the 2.5 fps burst. The Canon 20D is 5 fps up to 23 JPEG images and the 30D brings the internal buffer to 30jpeg. The XTi is 3 fps up to 27 jpeg images. (according to a quick lookup on dpreview).
In your case, its a balance between fps, buffer size, and cost. if you can live with 6mp sensor the Nikon D40 with its "unlimited" seems to fit the bill quiet nicely.. not too expensive too. From Canon's offerings, think the older 20D fits the bill quite nicely. Compared to the Nikon D40, It has double the fps, provides 23 jpeg buffer, and has the 8mp sensor you originally wanted.
BTW... Can't Canon and Nikon be more creative with the camera designations? Sheesh... 5D, 10D, 20D, 30D, D30, D40, D50, D60, D70, D80...