Digitech makes the Jam Man Looper pedal too. It has a some features that the Boss RC20 XL pedal doesn't have. It's pretty divided as to which is better.
I've included links from each company so that you can compare if you like.

http://www.digitech.com/products/JamMan/JamMan.htm


To compete with the Jam Man Boss has a new looper pedal that will hold 15 years of samples. Just kidding. It's quite a bit though. It also has a lot more functions than the RC20 XL or the Digitech. The features kind of blow the Digitech away but the price is hefty.

http://www.bosscorp.co.jp/products/en/RC-50/specs.html

The good thing about having these new pedals on the market is that the older ones are now available more cheaply either used or new. If you can live with the limitations of the older pedals then you can score a pretty good deal on one which makes trying it out a lot less painful. I bought one only after seeing other players using them, listening to them and asking them questions about them. Some folks might not have that opportunity.

Still, if you are a stay at home/play alone player get one! It will improve your timing, give you new ideas galore and allow you save those ideas. For a reasonable price you'll get an instant jamming partner who only gets as buzzed as you do, always shows up, stays in tune if you do, never takes a break and won't argue with you or steal your girlfriend. Priceless!