As far as buying Bitcoins, if you want to get your cash in quickly (same day) to buy at a good price when it drops, there doesn't seem to be another exchange other than Mt. Gox that BitInstant supports, unfortunately. (Yankee or Gareth, are you listening?
I'm sure other exchanges would be interested in your services at this point.)
Some examplesBlockchain.info (not an exchange) also uses BitInstant to buy bitcoins for your wallet, but their price is currently the same as Mt. Gox's during the 12 hour closure, so I think they use a Mt. Gox account to purchase the coins for you.
CampBX takes Dwolla or KYC, but both take a number of days, less days if the funds are already in your Dwolla account, for instance, but it still takes time.
Bitstamp takes International bank transfer, so not really U.S. friendly for getting funds in to buy Bitcoins.
Coinbase (not an exchange) can only take deposits from your bank account directly into bitcoins, but that also takes time, and their own recent caveat is simply too much of a risk: you don't send dollars to the account and then convert, you can only send dollars for bitcoins at a pre-determined rate, or for now, even worse, an unknown future price:
How much bitcoin will I receive?
Due to higher than normal buy volumes, we are unable to provide exact price quotes right now.
Instead of pausing buys entirely, we decided to give people the option to purchase bitcoin at the market price in a few days. Once your USD funds arrive, we will exchange them to bitcoin at the market price at approximately Tuesday Apr 16, 2013 at 11:07AM PDT.
Note that you can cancel your order at any time up until your bitcoin arrive from the transfer history page.
The market price of bitcoin changes frequently. Below are some recent prices to give you an idea. These do not guarantee what the price will be in a few days.
Edit: Bitfloor uses LocalTill for cash deposits, e.g. Bank of America out of state deposit. It is usually confirmed in 30 minutes if received before 5pm. Supposedly, even Saturday morning deposits have gone through in 30 minutes.