I found this when searching for the best price for the Seresto collar. The purchase has to be made by 11/20/13 and rebate postmarked by 12/15/13. There is plenty of time, so take advantage of it now.
Flea & Tick Control: Seresto Flea & Tick Collars for Dogs
*To receive your $20.00 Seresto rebate, simply set a reminder and save! Visit SerestoRebate.com to set an automatic reminder that helps take the guesswork out of your pet's flea and tick treatment schedule. Once your reminder is set, you'll be able to download a mail-in rebate for $20 off your recent Seresto purchase. Schedule your reminder now at SerestoRebate.com. Rebate requests must include the online mail-in rebate form (fully completed) and the receipt for product purchase. Product must be purchased by 11/20/13. Rebate requests must be postmarked by 12/15/13. Two rebates maximum per household.
Please allow 6-8 weeks for rebate check delivery.