Zazzle - I use zazzle to order my own magnets, since they seem reasonably priced. The magnets are hefty things, not just a magnetized business card. The kind you actually buy in stores nice. I don't really sell anything there, so I can't comment on any of those aspects, but I do offer notecards and magnets.
CafePress - one of the first sites I added my art, mainly for notecards, but I got too crazy with the other merchandise, so I added tshirts and some other items. Honestly, I can't tell you what's there right now. The website became too time consuming and confusing to me...too many choices muddled my mind. I think it's easier now to navigate, but I haven't taken the time to play around. I did sell a few things there, but I think mainly tshirts.
Fine Art America - one of my favorite places because of simplicity. It's just a site to sell/buy prints, originals, and cards. Period. I have most of my art there (which isn't saying a whole lot). It does not have any of my earlier pieces - either because I don't have a high resolution image to upload, or because it didn't make sense to put a portrait on there if I sell prints. To be honest, I've sold one thing, and it made my month! I mean, really, I'm an artist! I'm just another guppy in a sea of guppies and fish and...whales. Anytime someone takes time to look at my art (in a good way) makes my day.
EDIT: In order to create this post, I had to go to my websites to get the links. CafePress has updated quite a bit! I may have to add more stuff there, but I might take out those aprons...