There are some noticeable differences, but unless you're building something crazy, there's no reason to spend a lot on a header. One downfall of the cheap headers is that they tend to have fitment issues and aren't very strong. As for power gains, you wont notice a lot just from a header. It all depends on what you plan to do with your car...
Great:
http://hondamarketplace.com/zerothread/2027262
http://hondamarketplace.com/zerothread?id=2052395
Good:
I honestly cannot think of other companies that make headers....i've been out of the NA business for over 2 years
Meh:
http://cgi.ebay.com/ebaymotors/94-01...QQcmdZViewItem
-According to CivicSpoon, Pacesetter sucks...i can't argue with that logic