What is the value of 1 bitcoin in USD, today? Where can the exchange rate be looked up?
Very simple. Go to google and type: BTC to USD
A nice box with the current exchange rate should appear on your browser.
The price is constantly changing so this answer will vary quite a bit even within a day.
At time of writing (Nov 2015) the price is $375.40 per 1 bitcoin.
$1.00 should be ~0.0027 bitcoin.
You can check price at anytime by going to: http://www.coindesk.com/price/
Price per USA dollar in bitcoin would just be ~ (1 / bitcoin price).
My favorite is Tradeblock markets, shows live rates for various exchanges, and converted to USD