Laptop Connect rents Next G USB devices; you order online and they’re posted in a reply-paid envelope, which you use to return at the end of the loan period. The minimum-length rental is 3 days, which will set you back $59.20. There’s a one gigabyte a week limit, but in a travel context trying to download a whole TV series probably isn’t wise anyway.
If you’re planning a trip to a remote area but can’t see a long-term need for a wireless 3G connection, that could be a useful solution (especially given Next G’s extensive Australian coverage; it’s not much of an option for an overseas trip though). If you know of any other similar services, share them in the comments.