A lot of people on a budget use a 5 channel amp to bi-amp the front speakers and power the center channel. Using external amps for the front and center channels lightens the load on your receiver, allowing for a little more power to your surrounds, which is plenty for most of us. The XPA series from Emotiva is very popular, and considered to be a very good value.
http://emotiva.com/xpa5.shtm
or a little easier on the pocketbook
http://emotiva.com/upa5.shtm