I bought the Foto-Tip loupe from Ebay. I'm extremely happy with it. It's a piece of plastic, don't spend more than $100 on one. The connection is solid through the magnet. Be wary of gear snobs on this forum. While I agree that you have to be a snob on most of your camera gear, this is an accessory that does not require a lot of cash like nice lenses, etc...
Was that for use with the 7D or 550D? I've heard they're fine for the 7D, but a little too small on the 550D.