Several good choices in the $100 range. For fear of being a fanboy, however, I will agree with Sina that Polk Audio is the way to go.

Having said that, just about every major manufacture has a set of coax speakers in the $100 range....Infinity, Polk, Alpine, Rockford, Memphis, Pioneer, MTX, and more.

If you really want to do your homework, grab 3-4 of your favorite CDs, and go visit a few shops in your area. Listen to music you know well on different speakers. See what sounds good to you, and fits your budget. Remember though, how your hear things a given sound room, is NOT necessarily how it will sound in a car....most speakers will sound BETTER in a car compared to a sound room. I stress, most, not all.

We all have our favorites....

just my opinion.