You didn't mention where you're geographically located, but for UK users, I've found the service at speedybitcoin.co.uk to be very quick and reliable. You specify a receiving address, and whenever you send a bank transfer using particular details, you receive Bitcoins at that address based upon whatever the current Mt Gox exchange rate might be, less a commission. If you write and ask for a 'tailored account', you can get the commission reduced and the daily limits increased without a problem.

One caveat: since Mt Gox prices have been out of whack since their announcement that USD withdrawals would be temporarily suspended for two weeks as of 20 June, I wouldn't necessarily use any service just yet that relies on automatic quotes from Mt Gox.