There is a FREE Taco Bell regular sized Limeade Sparkler coupon in our local Sunday newspaper (back page of RedPlum insert), no purchase required. It expires 11/25/10. There were also tons of Buy any product get a Limeade Sparkler FREE or Buy a Sparkler Get one FREE coupons too.
I had the Cherry Limeade sparkler last time we had this coupon and it was really really yummy. Plus it makes for an inexpensive lunch — just add a .99 taco or two with this coupon!