Hurricane Electric has it's own lines running across the US and to Europe, but they also have lines from other ISP's/upstream providers. They have direct connection service ranging from Fractional T1's all the way up to 10Gbit, so they've definitely got the pipes.
If you are looking for colo/dedicated service, go through Hurricane Electric or one of their resellers. Their techs are friendly as can be. Not that I need to talk to them that much, but when you colo and you don't choose hardware wisely...
While it's hard to speculate what everyone's "commitment levels" are, or what they're "using", i'll add to what's already been mentioned here. This is by no means a complete list, and relies primarily on the claims of these companies, not so much on inside knowledge:
As for colocation, it obviously goes without saying that every national carrier out there will do colocation if the price is right. The ones with the most robust colo offerings are Level 3, Wiltel (the transit sucks, but their facilities are ok), Savvis, Cogent, XO, etc. Then you have the guys who are doing their own thing inside Equinix DC's, like nLayer and mzima. I believe that makes more than 20
Utilisation rates at peak usage is more important than absolute total capacity as long as it's decent enough. (1gbit and above) You should use that as a metric rather than just outright bandwidth capacity which can be misleading.