Huh. Odd. They seem to have taken the partners list off their site. Google found a few outdated pages, but there's no list.

Most domestic airlines and many international carriers are partners, I believe. There's usually a fee to collect miles which often (not always, but often) makes collecting miles a bad deal (you can buy the miles directly from the airline at the same or lower price) unless you've applied a bonus mileage coupon or something. The fee usually isn't charged on foreign airline partners and on other partners like hotel programs.