For my really serious work I send it out to Calypso in San Jose, California and let them use their $500,000, two-ton printer.
See Calypso's site for particulars. They charge based on square footage, material and how much of the preflight work you're willing to do yourself. As I recal they use the Cymbolic printer, which weighs almost two tons!
I ask for Lightjet prints on Fuji Supergloss material. They print any size up to 50" wide by however long you want. They charge by the square foot and the smallest print is 16 x 20." If you want smaller prints just gang them together and cut them yourself.
SuperGloss isn't paper: it's polyester that looks wet and almost 3-D when lit properly. It costs a little more than the regular Fuji Crystal Archive paper which they also use if you want. You get the file to them via CD or FTP (or email a JPG) and the UPS man brings your prints. They have three different prices:
Their most expensive service is if you send film and they have to scan it. That's their "Professional" service. They do all the artistic interpretation in printing, which if you're an artist is the last thing you want.
Much less expensive is if you send them a file, the "Standard" service. You send them whatever you have and tell them what you want. They do a little formatting to your file and print it. This is the best way for most folks. You can send them files from any source like digital cameras or film scans.
A little less expensive and the best alternative for artists who want to do it all themselves is the "Preferred" service. I use this. With this you do all the scanning, file preparation, profiling, conversion and artistic work. They just jam your file in their machine and return whatever comes out. If you're good at computers, have a reasonably well calibrated system and can follow explicit directions to send a 304.8 DPI , 8 bit RGB TIF converted to their color profile then this is the cheapest and best way to get exactly what you want. If any of this makes no sense to you then use their Standard service, or read their clear applications notes at their site. You don't need a printing workshop to learn this.
See my B/W Printing page for how to print serious B/W.