I use non-insulated Level 6 Military Issue rain pants--Trouser Goretex ECWCS
$45 on Ebay, brand new with tags
Wore [url=http://www.aerostich.com/suits/jackets-pants/ad1/ad1-motorcycle-pants.html]these on a 10,000 mile 'round-the-US trip a few years ago. Kept me dry, comfy and safe in all manner of downpours. Possibly a bit overkill, depends on your intended usage I guess.