This freebie from Nov 2013 has returned!
Walmart has four different batches of to choose from – teen, new mom, active woman, and sensitive bladder – but you'll have to click on the middle circle in the top right to get all the options to appear. Clicking on a free sample button on any other tab will result in going directly to a signup form for a specific sample pack, whereas clicking the freebie link in the image above will let you choose.
Sadly they've ignored the single guy demographic. Though that won't stop me from requesting and adding these to my questionably large collection of feminine products!
EDIT: The signup form seems bugged now, howeverlooks to be submitting well.