Alpine is always a good choice, the new V-12s seem to be very nice [I haven't owned one myself yet though]. I'm a huge old school Alpine guy and still run a nice 3553 and a 3550 as well.
My new favorites in the mid-price, good quality range are Cadence, Cross-Fire, and Planet Audio. I've got a Q3000 2 channel Cadence and my brother just picked up a Q4000 4 channel, very impressed with both for under $200 each.
Take a look at
www.nexxon.com, they have about anything in car audio you'd ever want with excellent prices too. I buy all my stuff local, but use nexxon for price comparison and info all the time.
For low end stuff, Power Accoustic is about the best I've used- FWIW.