You don't mention where you are.
To receive a direct deposit you'ld need your own account number with a financial service. There are currently no financial services that have a direct path to Bitcoin.
In the U.S., if you have a bank account, you can simply do a Dwolla transfer from that account and from there do a Dwolla account-to-account transfer to Mt. Gox or Camp BX to buy coins.
If you don't have a bank account you can use a prepaid debit card type of account which has direct deposit capability, and do the same thing with a Dwolla transfer. I believe Western Union's prepaid debit card allows this as does Walmart's MoneyCard. [I'm not 100% sure that you can set up ACH to pull from your debit card account though. If neither does, then I think American Express's Bluebird prepaid card does. ] Coming soon are mobile-only bank accounts like Green Dot's GoBank which will allow Dwolla to pull funds via ACH.
Coinbase also can do an ACH pull from an account however their service has tight limits while it is trying to keep up to market demand.
In the EU, Bitcoin-Central has described how it will have EUR accounts with a financial partner, and that would be a way to receive SEPA payments directly to the accountholder's exchange account.