Infinity will by far be the cleanest sounding unless ur wanting to pay alot. You can get them at pretty much any local audio dealer (circuit city, tweeter, etc). I would also recommened infinity kappas if u wanna step up and spend a lil more. I bought my infinity 3 1/2's from circuit city 5 months ago and wasnt expecting much at all cuz i only paid like 40 - 50 bux for them and they r awesome lil things. Crisp highs and great mids but dont expect to get much bass from such a small speaker. I in fact put bass blockers on them so they wouldnt blow. Hope this helps
I had Infinity Kappa's in my Olds for a while and the tweeters were a bit too nasty for my taste. I replaced them with Boston Acoustics FX3's and I love them. Smooth and mellow with better low end than the Kappas.
Kicker and Eclipse also make nice 3.5's. Go to Tweeter and listen.