If you have a Sam's Club membership, I highly recommend Image Plus cardstock. It is 110 lb. You can get 250 sheets for only $7.23. I use it for card bases, and also for stamping and coloring images.
It is available in the Sam's stores and also online:
GP - Image Plus Card Stock, 110lb, 8-1/2 x 11", White - 250 Sheets - Sam's Club