a midweight softshell pant is extremely versatile and comfortable. Stand out products are:
Patagonia Guide (now called the Alpine Guide)
Arcteryx Gamma AR
having a super light full zip rain pant as a backup for when it's wet (NOT for when it's too cold to be actually wet) results in a more comfortable system. Stand out products:
marmot precip full zip
arcteryx superlight alpha fullzip whatever-it-is
the super light full zip eVent option that's not on the market yet...
Most of the time you'll find yourself grabbing the softshell pants. When the freezing rain comes in and looks like it's going to stay for a while, you have the shells.
I suppose a viable combination option is to go for the mountain hardwear synchro pants. Not quite full zip but if you dont have skis on they'll still get the job done. Waterproof and warm.