FS2004 or FSX? There are some for FS2004, but they're really hard to install and fly like airplanes, I believe. If you don't mind spending $25 dollars, you can get HeliTraffic 2009 by Flight1. HeliTraffic 2009 works in FS2004 and FSX, and gives a pretty great experience of many AI helis flying around. They actually fly like helicopters. 

http://www.flight1.com/products.asp?product=helitraffic