My dear sweet son is going to spend the winter in Hawaii bicycling the islands (must be nice). He isn't interested in establishing a banking relationship when he arrives, so I am wondering what is the best/safest/cheapest way for me to get the occasional cash infusion to him.

Wire transfers would be the best and safest, but maybe not the cheapest. You could get a supply of depsoit slips for his account and mail in deposits or FedEx deposits if they needed to get there quick.

I would estimate we are two years away from having a mainstream way of allowing customers to initiate their own ACH transfers between accounts at different banks thru online banking and also thru ATM Networks.

You could also use your bank's online Bill Pay system by designating his account as a "payee" just like you would for your electric bill, but that would be, most likely, a painfully slow, non-electronic process, slower thatn just mailing a check yourself.

One other option is if they had a large National Bank in Hawaii that they also had in your neck of the woods. Then you could add yourself as an owner on his account and just make online transfers thru online banking, but I am not sure Hawaii has banks that also exist in the mainland.

If he doesn't want a bank account there, using funds transfer providers like Western Union or MoneyGram would make sense.

A lot of banks are promoting new ways to send money to relatives with little or no charge. It's really nothing more than getting an ATM card in your son's name as an authorized user and mailing him the card to use at his local bank in Hawaii. He could take the cash out at an ATM and deposit it into his own account. The only fees are ATM fees which are much less than wire transfer fees.

Your son could simply open an account at home and access it with an debit/ATM card there. Another option is prepaid debit and credit cards. In both cases, you could replenish the account easily.

P.S. Are you considering adopting any additional children?

I agree with Cub Dave about wire transfers somewhat. There is a fee for you to send and a fee upon receipt with most banks ( I've worked in wire for many years but not the operations for sometime). One of the draw backs is that many banks will no longer initiate or pay to non-customers due to AML/BSA, too much trouble.
I have a citibank card and I can initiate SWIFT transfers (wire transfers) to almost any bank in the world. I believe the fee is around $5.00 domestically. I just log into Citibanks site and the amount is charged to my card. We had a small business overseas and found this to be the best for us since my bank would have charged me $45.00 (because it was International Citi charged $15.00). Or as was suggested, use an ATM card, you can fund his account here or let him access your account with an ATM.

It would be easy and fairly inexpensive to have a joint account at home and he could have a debit card on the account. You can put money in and he can make debit purchases or withdraw cash from an ATM. With the account near your home, it is convenient for you and it matter where he is.