If I am declaring foreign income and also excluding using form 2555, do I need to attach any income statements or proof with my 1040?

Also, we are required to report values in US dollars, and the exchange rate fluctuates quite a bit. What should be date on which we use the exchange rate? Can we use the exchange rate as of 2008/04/04?

If we need to find exchange rates in the past, where do we get it?

No you don't attach any proof. You keep with you in case IRS wants to know.

Calculate based on when you actually received the income. If you were an employee and you received 12 payments, then for each payment you will use different rate as on that date.

Search Google U.S. to... conversation rate