Well since everyone has come in here and given the easy answers already, I'll try to muddy the waters just a little bit.
There are a handful (but not many) of outlying ones like the Mark Twain bent and some of the Supremes that I believe are system pipes but not clearly marked as such. In terms of estate pipes, it gets real complicated since they have been marked a variety of different things over the years. If you are in the estate market, then you need to do some homework.
In simple terms of widely available current production pipes, the System Standard and System Deluxe are the "System" Pipes. The others are so rare and uncommon, that you won't run into them unless you hunt them down and pay handsomely for them (i.e. Supremes, etc.)
Now P-Lips are an entirely different issue....