Buy when there's blood in the streets (assuming the fundamentals are still good, which it looks like they are...) http://www.bitcoinpulse.com/
Can you explain what you consider to be the more important fundamentals for bitcoin?
2. Number of users SPENDING bitcoins to purchase goods
3. Number of merchants accepting bitcoins for goods
4. Total $ value of bitcoins being spent to purchase goods
5. Total $ value of bitcoins being spent to perform international money transfers
6. Amount of press (bad press OK, good press is worth much more) that bitcoins are getting as it drives 1 and 3.
I'm sure others have their own list of fundamentals.