Vibram Five Fingers. Or get some "Chuck Taylors."
I wear the Five Fingers and I wouldn't wear anything else. In addition, they are so sexy that women follow me when I wear them to the grocery store. Seriously, they are awesome!
Why you ask should I work out with naked feet or something similar?
First of all, working out barefoot will make your feet stronger more mobile. As important, working out with kettlebells barefoot also requires that you maintain awareness at all times and maintain proper body alignment and it all starts at your base-----Your feet.
Kettlebell work requires foot awareness in almost all exercises. You have to be balanced and powerful and "root" your feet to get the most benefit.With shoes and socks on, awareness of the feet is almost non-existent.
Practicing kettlebells, or anything else for that matter, barefoot you’ll become not only more aware of your feet but a better judge of your alignment. You’ll have a better feel and view of your feet in relation to your knees, hips, etc. Remember, everything starts with the feet. If you’ve ever visited an orthopedist for knee pain, the first thing he does is take a look at your shoes. The feet can tell a story…how a person moves, stands, etc. Healthy feet are central to healthy alignment.