Nforce2 chipsets are well liked. Nforce3 not so much. The nforce4 due out in early 2005 is supposed to be really good.
Via kt400 is good and solid but nforce2 outperforms with the right motherboard.
One of the best boards going is the Abit NF7 nforce2. They are getting a little old now but still very popular. They are extremely well priced now too and a much better board than the Asus.
Check out the motherboard rankings and reviews here.
http://www.motherboards.org/ranking/motherboards/AMD/