They do a wide variety of sizes and weights and colours so pretty much fit most needs. As a secondary supplier of card I use Amazon in the UK which has several different grades of card at reasonable prices.
Eco card is my main supplier though and I've not yet been disappointed with the quality. It's also one of the very few places I can get 1mm card from - who don't mind shipping to my rock. For whatever screwy reason a heck of a lot of suppliers in the UK seem to think I'm in one of the two arctic circles (or possibly in orbit) so "don't ship overseas"... *sigh*