yes, wonderful coomax socks -- great idea
how about:
those earmuff where the band goes behind your head and under your hair -- that's what i wear when it's not cold enough for a hat
walking music CDs if you listen to music
cross-training workout DVDs - yoga, pilates, light strenghth training and accessories (stability ball, hand weights, yoga mat)
reflective gear if you walk outside in the dark
massage gift certficates
heart rate monitor
packets of GU in your stocking
Marathon for Mortals book
journal if you are the journaling type
ok -- my thoughts dried up here! hope a couple of those sound good to you