What's currently the easiest way to buy bitcoins specifically for USA citizens?
is it
http://coinbase.com ?
It depends on where in the USA you are located.
For many, LocalBitcoins.com is the easiest way.
If you don't have a reliable trader nearby, then I'd say
BitFloor is the next easiest.
Both of those options have the benefit of allowing you to trade with cash. No need to "link" your bank account or initiate a "wire transfer" with your bank.
Tangible Cryptography allows cash deposit as well, but you have to have a working knowledge of PGP encryption and signatures.
If you want to go to the trouble of linking bank accounts or wire transfers, I'd say CoinBase, BitMe, and MtGox are the next three easiest (in that order).
If you trust me, and want complete and true anonymity, you can send cash and a bitcoin address to my PO BOX and for a 10% fee I'll do all the work to convert and send the bitcoins to you. Doesn't get much easier than that, you don't even have to leave your house if you happen to have the cash on you (As indicated in my signature, this service is on hold while I am traveling between March 9, 2013 and March 28, 2013).
If anonymity isn't important to you we can work out a cheaper fee and other payment methods (Postal Money Order for instance).
Personally I find #bitcoin-otc to be the most complicated, but I'm sure others find it to be quite easy.
EDIT: As of 2013-04-17 BitFloor has ceased all operations.