Twin Lever Metal Bottle Capper from MoreBeer.  I have this capper (See: Brewing Your First Extract Beer, Illustrated Step by Step).  It works well and has a nice firm feel when capping.  Because of the metal construction, I would probably choose this over ubiquitous Emily style level capper.

In action: Bottling a batch of Zythos IPA

Product Description – Here – Use coupon code BEERDEAL to get this discount.

Availability: This is a More Beer Deal of the Day. Quantities are limited. Check the Deal of the Day section – Here – to see if this is still available.

Twin Lever Metal Bottle Capper B481 – $15.99 $11.99 + Free Shipping with a $59 order