Heres a few transaction scenarios for you, you can also check out the walgreens thread for more great ideas.

Transaction #1: Shave Gel
Sale: Schick Hydro Shave Gel $2.99
Buy: 1 Schick Hydro Shave Gel
Pay: $2.99 + tax
Get: $3 Register Reward.

Transaction #2: Dental Care
Sale: Colgate Pro Clinical Toothpaste, 4oz.
Buy: 1 Colgate Pro Clinical Toothpaste, 4oz. + One small filler item
Use: Colgate Pro-Clinical 4.0 oz. Toothpaste variant $1/1 (5-1-10) SS-4/11
Use Register Rewards: $3 from transaction #1
Pay: Price of filler + tax
Get: $2 Register Reward

Transaction #3:
Sale: Tylenol Cold or Allergy 20 or 24 ct or Liquid 4 or 8 oz OR Sudafed 16 to 36 ct, Nasal Mist .5 oz or Liquid 4 oz (limit 1 Sudafed D) OR Benadryl 18 to 24 ct, 10 pack or Liquid 4 oz
Buy: Any 2 listed above
Use: Zyrtec, Benadryl, Visine, Sudafed PE or Tylenol Sinus family of products, any $5/2 (7-31-10) RP-4/11
Use Register Rewards: $2.00 from Transaction #2
Pay: $2.98
Get: $5.00 Register Reward

A great way to roll this last $5 register reward is to do transactions #1 and #2 together. You wont need a filler and you end up paying .97+ tax and getting a $3 and $2 Register Rewards to roll into another Transaction #3

Other Great Deals:
Diaper Deal Transaction: (only a good deal if your brand loyal and need diapers :p)
Sale: Pampers Twin Pack Cruisers Dry Max Diapers, $18.99
Buy: 1 twin pack
Use: Pampers Swaddlers Sensitive, Swaddlers, Cruisers or Extra Protection Diapers, any $2/1 (4-30-10) RP-3/14
Pay: $16.99 +tax
Get: $4.00 Register Reward
There is also this Pampers coupon: Pampers Diapers or Pants, any $1.50/1 (4-30-10) PG-4/4

Snuggle Fabric Softener 32 loads $3.99
Use: Snuggle Fabric Softener Liquid, 32 lds or larger, or dryer sheets, 70 ct. or larger. $3/1 (5-2-10) RP-3/28
Pay: .99+ tax

Bayer Breeze 2 or Contour Blood Glucose Monitor $14.99
use: Breeze 2 or Contour meter from Bayer $30/1 (4-30-10) RP-10/25
Pay: Tax

Questions about how Register Rewards work?Go here for the answers.