Boston Acoustics SX65

Excellent speakers

These are excellent coaxial speakers. They'll sound great running off an aftermarket headunit or an amp (I was pushing 75 watts to each easily). Naturally, you'll get the most detail from an amp, but the clarity from the headunit was great. My music sounded very natural on these, though I'd recommend you have a sub with these speakers for the best experience. Installation was a pain, but only because these are technically 6 3/4" speakers, though they'll fit in 6 1/2" openings with little to no modification (of the opening). For the price, these are great speakers.

Great sound in small place

If you want good sound quality then make sure to go with Boston Acoustics. These speakers work great for me and they are very well built. I had an issue putting these in only because they are bigger then the actual slot would allow for my door. I had to do some heavy modding to get large gauge wire to them and to mount them safely. In other words as long as your not modifying the speaker, don't be scared of modding the car, screws, etc. to fit your car! You won't be disappointed in these! They can crank some sound too without too much distortion at all.

alright

I have to sucker hooked up to a MB Quart 4 channel amp. The sound is awesome when the tweeters work. After about 5 minutes crankin it to a good song the tweeters seem to stop working. If you let them "cool down" after a while they work fine again. If your going to get these, I recommend you put a small amp to them or connect them to a high power head unit..

Sound Great

Put these in the rear doors of a 2001 Toyota Sequoia. I am powering these (along with component SX60's up front) with Kenwood DNX-6140 head unit, no amp. They sound great and the Kenwood has not problem driving them.
The size is a little weird; they're between a 6.5" and a 6.75" speaker so most adapters and standard rings don't work. But with a little tweaking you should be able to get them in and you won't be sorry.