Do a forum search on Speedplay. They've been discussed many, many times.
In a nutshell: Frogs and X-2, excellent if you need or prefer a lot of float. Very easy to clip into and out of. Speedplay Zeros did not work for me at all; could not clip in. Have not tried light-actions but have heard that they are a lot easier to clip into than Zeros.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow