go with a borla turbo muffler its what i got on mine- sounds great- im getting headers/y-pipe w/ a cut-out- exhaust dont do much for performance but a y-pipe will on the s10's y-pipe is most restrictive part next to the intake manifold- mine is a 2.5" exhaust from the y-pipe back right now-

 

I've got a Spintech Sportsman with no cat and side exit on my Blazer, sounds pretty good. You can pick them up for around $80 and have someone bend up the pipe.

 

The Dynomax ultraflo cost the same amount and they are straight thru.