What is a cost-efficient, fast and easy method of transferring btc between own computers? I use a few computers and would like to perform bitcoin transactions from any of them. Thing is, I'm not very fond of the idea of paying the fee and waiting every time I want to transfer the coins from one computer to another. Is there any other simple, convenient, easy "out of band" method of transferring coins between computers?

(I realize an online wallet service would solve my problem but I really don't like the idea of trusting a 3rd party with my bitcoins)
[Edit: Read comment as to why this is not a good idea.]

You could just store the wallet.dat file on both computers, which contains your entire wallet. Then both computers will be able to spend from the same wallet.

Do make sure to copy the wallet to the other computer from time to time: if you don't synchronize regularly, the balances might start mismatching because the private keys are no longer the same.