A BIG HUGE thanks to Victoria for this incredibly helpful information. I've been struggling to do this for the two years I've lived here (like she says in her post, I too still have student loans & a mortgage to pay in the US. ugh.). Hitting the ATM while in the US to take money from your UK account, only to turn around and deposit in the US is certainly *not* ideal. Looks like Victoria has found a way to easily, quickly & cheaply transfer money from your UK Bank to your US Bank (or Canadian...) using a service from company called ukforex.co.uk.
I haven't tried it yet, but I definitely will in a few months-and will let folks know how it goes.
As a somewhat related aside...you may want to read up on what amount can be transferred from the UK to the US before raising eyebrows with your bank-and possibly have to pay tax on it. In speaking with my tax adviser about this previously, I was told to 'keep it minimal'-ie less than $10k a *year* would be good. But, above that, I'm sure the bank-and the IRS may start take notice. Or not. Depends on your situation, I guess. But, worth a mention, nonetheless..