This is the most comprehensive all-time Bitcoin price history chart you will find online. Updated daily.
Price data begins as early as 2010-04-25 at $0.003/BTC, using the daily volume-weighted trading price of the first Bitcoin exchange, BitcoinMarket.com (PayPal USD trades). It actually started operating on 2010-03-17, however data before 2010-04-25 is—to my knowledge—not available. Price data for 2010-07-18 and later is from the CoinDesk BPI.
The chart is interactive: