Crutchfield is good for customer support for the beginners but they are a little high priced.
Sonicelectronix.com has really low prices but not a huge amp selection. Free shipping on all subs. and BOGO Kicker Comps
Loseyourhearing.com is not bad either

Onlinecarstereo.com. Decent prices from what I've seen, although I usually don't buy new equipment. Its just not worth it. The sub for the Regal and rear 6x9'* for the Bonneville I have were used off of a guy on w-body.com, the amp was used off ebay, and a bunch of other random stuff. Car audio loses its value so quickly that its really not worth buying it new unless its something like a head unit or wiring.

onlinecarstereo.com

I like to buy new, but I don't buy often either. My last Pioneer Premier HU lasted 7 years. But I learned to stay away from motorized faceplates.

I've bought from both www.onlinecarstereo.com and www.sonicelectronix.com

OLCS though is pissing me off right now. Two items I ordered have been back-ordered for a month. Just gonna buy them off eBay I think.

sonicelectronix and SMD forum members

Sonic, Darvex, KnuKonceptz, WoofersETC, Sundown, those are the main one'*

yeah knukonceptz is one I use as well.

sundown FTW and i see ya also have a 1500. i love mine and won it on SMD system of the month lol. i buy alot of stuff used on forums and/or woofersETC. they treated me good every order. also check out
http://secondskinaudio.com/
http://www.mobilesolutions-usa.com/
http://www.db-r.com/sell/store/

Yeah buddy! I'm very happy with my Sundown amp too, it'* a beast of an amp for sure! I bought mine BNIB off a member on DIYMA, it had never been powered up before I got it and it was about half of what they go for retail so I was happy.

All of my deadening is SecondSkin thanks to two free giveaways on SMD That stuff is kinda pricey so I saved a few bucks there. I hope I never had to deal with db-r (not cause they're bad to deal with cause i've never heard that) cause it probably means my amp isn't working as it should and I need to send it in for repairs. Mobile Solutions, damn they're expensive!

I take back what i said about sonicelectronix they do have a good variety of amps i just missed em. Did u guys see the $10,000 Kicker WarHoarse? WTF. I'll stick with my Modified PPI PCX2400