A very good place to judge preamps from is the following website:
[url="http://www.basstasters.com/"]http://www.basstasters.com/[/url]
Lots and lots of clips to listen too. There are plenty of preamps out there.
As for the poweramp side of things, I personally believe that it doesn't make [i]that[/i] much difference in shaping your sound. You can spend lots of money on a power amp if you wanted, but there are some very good value ones out there. I use a behringer one, it's not gone wrong in 2 years. However brands such as Yamaha and QSC have some good value stuff out there as well and they are obviously a bit better quality.