I've been with GNAX / Net Depot for the last few years. You can co-locate there and the service has been rock solid apart from a lightning strike DIRECTLY on a transformer. But they have dual power inputs and gas backups on site. They're located in Atalanta.
http://gnax.com http://gnax.com/network.php#gold http://netdepot.com (send an e-mail and ask about colo as this is the dedicated renting site they run)
Also, if you're looking for more info check out the Colo forum on Web Hosting Talk:
http://www.webhostingtalk.com/forumdisplay.php?f=44