I have a small vibrating massager that is a little bigger than my palm, although it is easily used one-handed. It is shaped like a giant ladybug. The wife and I use it for back massage.
The other day when I finished her back, I ran it across her tuckus and the back of her upper thighs. She enjoyed that, so I moved it down to the back of her knees. She commented that it tickled slightly. (Just imagine my evil grin upon hearing that!) So, I laid across her thighs and moved the unit down to the upturned soles of her bare feet.
She never said that it tickled... she didn't have the chance. She immediately shrieked and laughed so hard I thought she'd buck me off! I used that puppy on both soles for about five minutes, to very good effect.