I haven't started looking myself for amps or speakers for my xD but I want to know if there are different amp sizes. How small do they run or are they all the same size? I'm thinking of getting a smaller one just because I don't care for the standard size (or what at least the bf has in his Eclipse) and I'm not really in to pumping out a lot of "thump" to the speaker(s).

Personally I don't want there to be a big box in the middle or one of the two sides in the back but I would rather try and.. build it in to the back of the car in an area I have in mind. Though doing that is beyond my abilites ;)

So, do amps come in one size or are there smaller amps? Does having a smaller amp effect anything important that a standard wouldn't?

generally a low power amp will be small.are talking sub,subs,speakers or what?

Subs more than speakers sorry hehe. Not sure if I want a 10 or 12, or two 6s in the back. No idea =\

well depending on how much room you want to take up there are lots of options.check out crutchfield.com and look around they have all the dimensions and everything.or even edesignaudio those guys are awesome they have an online chat set up and they are very helpful.