Planning Poker and Affinity Grouping in Software Development estimating.
I have used both methods and find the Planning Poker (Fibonacci sequence) better. I feel it draws out more thought and conversation by all players in the process. Whatever method you select, the key is to review your estimations after the project is done and catalog the errors and successes of the estimations. This will improve future estimations.
The article in PMI describes both methods in detail.