Postal Money orders aren't reversible. You can also cash them at the post office AFAIK. 2nd day Priority mail is fairly cheap.
I'd say Western Union but their fees are ridiculous but they are less than $50 that Paxum wants for a wire transfer.
I don't know much about MoneyGram.
USD Volume on TradeHill is drying up like a cowpie in August because Paxum charges $5 to get money into their system, so all the USD is going through Dwolla into MtGox
MtGox may be taking losses from Dwolla reversals but not telling anyone about it . . .
I wonder how the "deposit cash at your local X bank" system works, and what fees are involved. I haven't been able to find anything describing it.
I think postal money orders can actually be cashed for U.S. Currency at a post office? Not sure if there is a limit on how many of these one person can cash:https://www.usps.com/shop/money-orders.htm
Update: using postal money orders is a good way to get investigated for money laundering:https://postalinspectors.uspis.gov/radDocs/pubs/ar01_06.pdf