Printspace is great if you need prints from digital files and you know how to prepare those files for printing (they require you to convert your files to their profile and then add Canvas Size in Photoshop if you want white borders). They do digital c-types and inkjet.
If you need more handholding - i.e. if you want to sit down at a computer with a real human printer and discuss how the file should be interpreted - then try Bayeux, Genesis or Metro. But it will cost you, compared to Printspace.
If you're after hand-prints from negatives there are various options. For colour, Michael Dyer Associates are good. For B&W, Klaus Kalde.