Join Date: Nov 2007
Location: Twin Cities, MN
Bikes: 1987 Denti w dura ace (road)/ "cheap" Jamis (mtn)
It depends on what you want to spend.
I started off with Lake summer mtn bike shoes with booties over them. Thick wool socks and a hand (yes, hand) warmer on top of my toes. I got the hand warmers in a big package at Sam's club. It cost me $0.40 a day to use a pack of two. To keep them usable for the ride home, put them in a zip-lock baggie and squeeze the air out. They will be fine for the way home (and more).
That took me down to -5F. At that temp, my feet were cold by the time I got the 10 miles to/from work.
Now I have the new Lake winter boots (as of last week -$270. Thank God for tax money!). Those take me down to around 20F by themselves with regular socks. If I add the booties on them, wool socks and a hand warmer, it took me down to -15F (-30 to -40 windchill) last week very comfortably.
I use cleats on both set-ups, just FYI.
This is based on MY feet though. Results may differ if you have different feet