I had this same exact question two weeks ago!
Someone recommended
http://finerworks.com to me -- I've used it and am very happy with the service! The prints come out exactly like your digital file! The thing about this website is that after the first print, the rest are half off -- which means if the first one cost $10, the rest are $5, depending on how you order. Fast shipping, too - priority mail. No complaints..and a 30 day return policy. (Okay, now it sounds like I'm advertising for them). But anyway, that's what's been working for me.
I had my artwork scanned at kinkos and put on a CD as a jpg file. However, i think any camera beyond 10megapixels should provide quality prints for a decent size.
I just checked out iprintfromhome and it looks cheaper, so maybe I'll invest a little and test that out.
Good luck with your prints -- it is SUCH a hassle at first trying to figure everything out..but once they come in, it'll all be fine. :)