One that involves a spring and clamp like the Kyser,
http://accessories.musiciansfriend.com/product/Kyser-QuickChange-Capo-6String?sku=361600&src=3WFRWXX&ZYXSEM=0&CAWELAID=26024255
and those that involve a simple bar held in place by an elastic band, such as this Jim Dunlop model.
http://www.jimdunlop.com/index.php?page=products/pip&id=75&pmh=products/capos
I have both but generally use the Kyser. If you feel that the clamp gets in your way you might opt for the bar and band type. There are also clamp models with the mechanism that sits in a different spot. Like this Schubb
http://sonic.net/~shubb/deluxe/index.html
It's all personal preference.