What you want is polypropylene socks under a merino wool blend sock. Perfect for those 35-55 degree F rides.
http://www.amazon.com/Wigwam-Dry-Foo...ref=pd_sbs_a_4
http://www.amazon.com/Wigwam-Unisex-...rds=wool+socks
Polypropylene won't cause blisters and wool stays warm even if your feet get wet. Just don't dry your wool socks on high heat in the drier or they shrink badly. Tumble dry on low with a dry towel until the socks are just barely damp, then lay them out to air dry the rest of the way. Don't be fooled by cheap wool blends that are 70+% acrylic with just a bit of cheap wool mixed in. Get socks that are at least 50% merino wool. Merino wool shrinks less and is less itchy than most other wools. I don't recommend 100% wool socks as they don't stay up and lose their shape over time.