I'm going to order them from this website. We got the Mickey and Minnie ones for any engagement gifts we got and we'll just use them for random things too. I'm probably going to get Minnie ones for my shower thank you. There was a sale when I ordered so it was a pretty good deal. The paper is not the thickest, but the notecards are cute. http://www.expressionery.com/product.aspx?lineid=277&productid=1842
Just wanted to add that they are currently having a sale, it's 40% off site wide and free shipping using the code "holiday09".
They have wedding images too (a bride under girl and some bride and groom images under groups). I'm not sure what your style is -- they may be too cutesy for 'ya but I figured I'd throw it out there.
I made mine on Shutterly with a few photos from the Shower - one of me and my DH when we first got there, one of me and my girls and one of me and the cake. It really made them more personal.
This will sound weird, but I got almost all of my bridal stationery at T.J. Maxx! For some reason they always have really cute cards with brides on them that are usually really cute. I bet you that bridal cards are consistently the ones that stores have overstock in because a lot of brides just send out plain thank you cards.
I agree with the poster who said check out TJ Maxx and places similar: Marshalls, Stein Mart, etc. They are very cheap and remember it is more about the thought inside. Just look for something that matches your colors. If your shower was already a week ago and you haven't even ordered cards I would high tail it to a store so you can get to writring PRONTO!