Here's a link from an EarlyReturns email I just received to a 40,000 miles after $500 spend with up to 10,000 additional bonus miles with balance transfers.

Details: Frontier Airlines World MasterCard® with Annual Fee

-Earn 40,000 Bonus Miles after spending $500 in the first 90 days
-Earn Up To 10,000 Bonus Miles (1 mile per $1) with balance transfers in the first 90 days
-Earn Double Miles on Frontier purchases and 1 mile per $1 on all other purchases
-Low Intro APR on purchases and balance transfers for the first 12 months after account opening
-Redeem companion tickets for 5,000 fewer miles (subject to fees/taxes from $5)
-$69 annual fee