Enter the xPrintServer from Lantronix. It's a small iPhone-sized device (but a little thicker) that connects to both power and your corporate Ethernet LAN. it detects available printers (and there is a huge list on their site with supported printers) and makes them available, natively, to iOS devices on your network. I tried it at CES and, like they say, it is as easy as "Open the box. Plug it in. Print!"
At $150, it is not for the home user... You could just get a new iOS friendly printer. But it's meant for the corporate environment, and a single xPrintServer can support 7 to 10 printers, bringing the cost to just $15 per printer, which is less than an ink or toner cartridge!
The xPrintServer supports printers from HP, Toshiba, Xerox, Lexmark, Canon, Brother, and Epson as long as they are network attached (wired or wireless) but not USB attached. The iOS devices must be running iOS 4.2 or newer.