It's rare that I will actually go so far as to advocate a supply product (I have ripped up a few in terms of magnetic and screw cases that I didn't think were worth their asking price in these forums before...) but since I've finally had a really great experience - I will give a plug here for Perfect Fit Innovations. Check these guys out:
http://www.perfectfitsleeves.com/default.asp
Bottom line, bar none the best sleeve out there on the market. What I ordered was for graded cards (PSA), but they also sent a freebie sample pack of sleeves for top loaders, and other case sizes.
Ever get a graded card in the mail and think "boy, it's a good thing the grade is on the card inside and not the holder itself!" (?) I have, and am routinely annoyed by this kind of thing. Perfect fit lets you protect a slabbed card from scratches and dings in perpituity - their sleeves fit very snugly and have a high-quality gloss-like surface to them. They really do make your cards look slick. Way better than those "graded card bags", in any event - which are way too big. I think you can get those from Cardboard Gold or one of those outfits. They do the job but really looks sloppy in comparision to these Perfect Fits. Had been unaware of these until I recently got a PSA slab in the mail that had a card in one - and immediately I dug in and did my research and found their site. When I first went looking, they were backordered on the PSA size for a while, but re-stocked. 2 packs of 50 sleeves plus shipping ran me a tad less than $7. Wonderful deal if you ask me...