Walmart offers the NordicTrack 18" Massage Foam Roller for $16.58. (Sears charges the same via in-store pickup.) Opt for in-store pickup to avoid the $5.99 shipping. That's $5 under the best we could find for a similar one sold elsewhere. It measures 18" x 6" and comes with an exercise chart.

Update: Walmart now charges pennies more; however, Sears still offers it for $16.58 with in-store pickup.