I just went to CVS to take advantage of this one: 12 packs of Cottonelle are B1G1. In addition there are $.50/1 coupons for packs of the same size. The limit is 4, so naturally I brought 4 $.50/1 coupons with me so I could save an additional $2. Each 12 pack (double rolls) was $10.49 before coupons, so I paid $4.75 per pack or less that $.40 per roll.
Also, All You magazine has a $1/1 cottonelle coupon. Buy two magazines (which I think are well worth it - lots of coupons), and get two 12 packs for $4.25 each or $.35 a roll.