For promotional purposes, I had bookmarks made up via Overnightprints.com. Info for my YA novel was printed on the front and info for my short story was printed on the back. The bookmarks are thick with a glossy surface which I like, but the backside short story was off-center. On the web site, it's hard to tell how much off center it'll look, so it's best to have an image that goes all the way up to the bleed edges. I didn't want the text "La Claire Fontaine" to be cut off, so I couldn't set the image next to the bleed lines. Some people don't notice unless you point it out, but this is a lesson I will take with me for the next set of bookmarks I have printed.
I had a business/personal card made up with Vistaprint.com. I've used them before for other cards and haven't had a problem with them. The background color is a darker pink than what I saw on my computer screen, but I already figured that was going to happen. Either the web site states that the colors will be darker or someone stated it in a review. I don't remember where I read it, but you should keep that in mind for any site you want to use for printing business cards.
For nicer looking cards, I'm sure Moo.com would be better, but for the same price you get less than half the amount you would get with Vistaprint. I was debating on which one to use, but went with quantity instead of quality for these first cards because I wasn't using one of my nicer drawings and was planning on giving out more than the 50 that Moo was offering.
You can get nice rounded edges with the Moo cards and probably richer colors. I might go with them in the future if I have a really nice design drawn out.
If you don't draw, they have design templates you can use.