60lb. cover stock is my paper of choice (I've yet to use anything else). I found it interesting that all types of papers (i.e. bond, offset, cover, index, etc.) have different weights for the exact same thickness of paper. You would think they would make it easier than that. The "weight" is apparently the weight of 500 sheets of that type paper in it's "basic" size. So, for instance, cover stock's basic size is 20" x 26" while index's basic size is 25.5" x 30.5". Therefore, index is "heavier" than cover when the thickness is the same. Confusing enough? Here's a link to help you out.
Paper Weight - Conversion Chart