brenda Tharp:

"I had a client order a 16x24 of a fine art image the other day, one of my favorites from my Impressions of Nature series. After I stopped jumping up and down with joy, I had to get down to the task of having it printed. I don't have a large printer, so that meant having a professional printer do it for me. But that was easy, since I developed a great working relationship with a digital service lab a few years ago."

I get a bit of printing done, by an online photo printing bureau in this part of the world (amusingly called 'frogprints'). While I haven't yet developed a personal relationship with them, I'm more than happy with the quality of the prints. Also, I haven't gone any larger than 10 x 15 yet - just no need to do so. The important things are to send as lossless an image as possible, and to get the number of DPI right. Any good printing bureau should be able to tell you their recommendations for both of those. If they do, follow them. If they don't, ask them (and consider going somewhere else).