Rovair rents out pre-activated wireless broadband modems. We used it for coverage of CES in Vegas. Apart from the general lack of available bandwidth at the modem-infested show, the service worked perfectly and we'll be sure to use it again.
It works like this: you tell Rovair the dates you need them for, then select the exact model you want. We opted for the broad compatibility of Novatel's U727 USB modems, but there's plenty to choose from. Rovair mails you the gear, which arrives on the specified date.
When you're done, you use a pre-paid envelope to overnight it back to them. Staff were pleasant and personal whenever contacted.
There are a few things to bear in mind. First, you're billed until the time the return envelope is scanned by the mail people. So it's best not to dump it in an airport mailbox, which might not be checked frequently or on weekends. Find a person to hand it to, like a FedEx worker, hotel concierge or clerk at Kinkos.
Remember the stick's phone number, too. You'll need it in a pinch: Verizon's Access Manager download page is guarded by a form that requires it, and Sprint won't even talk to you if you don't know it.
Finally, a WiMax offering is a must this year: EVDO used to be the secret to effective CES coverage, but now everyone's got it, it's as slow as dial-up!