What size/kind amp do I need?

OK guys - Let me start off by saying, I am not going for a big bass system here, and I won't be using a subwoofer.

I will be using Polk 6.5 EX365's in the doors, and a Polk EX365 in the rear factory Bose box. I will probably be using the same in the rear panels beside the passenger seat, unless I can come up with something better in there (6x9's, etc.).

The Polks claim they will handle 180 watt's peak power, and I want as much out of them safely as I can get.

I am using a Sony Xplod CDX-C7000X head unit (and regardless of how much everyone else hates Sony Xplod stuff - I love this head unit, it has been excellent for the past two years) that has 50w x 4 output.

You can probably gather that I am just going for sound, not thump. If you read anything here that I should SERIOUSLY consider changing, then let me know. Like I said, I am happy with my head unit, so until IT convinces me otherwise, I am sticking with it.

So I am looking for the best for my money that's not overkill.
Thanks in advance.

Edit: And it is by no means impossible for me just to go with a 2 channel amp just to give more power to the fronts since I am going for sound mainly anyways and the rear is just noise fill. Just a thought.

Check out USacoustics.com they have some great amps at great prices. I think all the 4ch are less than $200 online usually. The 80Wx2 usually runs around $120 or so. And these are not inflated ratings, they are RMS @ 12.8V. I always suggest them for those with a HIGHLY limited budget. Bang for the buck, they can't be beat. I've never regreting getting mine and neither have the folks I've suggested them too. PM me if you need a place to procure these puppies.