An interesting agile time-estimating method agile.dzone.com/.../introduction-planning-poker

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Planning Poker is extremely simple to play while also being accurate enough to use for agile planning. The basic rules are as follows:

Each participant gets a deck of estimation cards representing a sequence of numbers. The most popular sequences involve doubling each card (0, ½, 1, 2, 4, 8, 16, etc.) or the Fibonacci sequence (1, 2, 3, 5, 8, 13, 21, etc.). The Fibonacci sequence is generally more popular.
The moderator presents one user story at a time to the team.
The Product Owner (or equivalent role) answers any questions the team might have about the story.
Each participant privately selects a card representing his or her estimate of the “size” for the user story. Usually size represents a value taking into account time, risk, complexity and any other relevant factors.
When everybody is ready with an estimate, all cards are presented simultaneously.
If there is consensus on a particular number then the size is recorded and the team moves to the next story.
In the (very likely) event that the estimates differ, the high and low estimators defend their estimates to the rest of the team.
The group briefly debates the arguments
A new round of estimation is made (steps 4 and 5 above).
Continue until consensus has been reached and the moderator records the estimate.
Repeat for all stories.