I have found regular two-strap binding better suiting my taste for comfort and adjustability. However for those who want to gain few seconds and don't want to get their butt wet, there are several rear-entry bindings on the market. Additional cons would be heavier than standard bindings and while the system is great on flat area you will have to use them as a standard entry in downhill situation.
Flow NXT FRX, 369euros / 2216g
Since 1996, Flow has developped rear entry binding and have a wide range of bindings (and price).
APO Team, 200euros / 2296g
Most innovative rear entry system, there is a video on the site.
K2 Cinch CTS, 199,95euros / NA
Here is a pretty good video showing how it works, there are three men bindings in the Cinch family : CTX, CTS and CTC.
SP-United /Voelkl Fastec, 199euros / 2140g