Take your pick...
1. FDPIX - Falling US Dollar ProFund
RDPIX - Rising US Dollar ProFund
2. RYWBX - Rydex Weakening Dollar Fund (leverage 2:1)
RYSBX - Rydex Strengthening Dollar Fund (guess what, also 2:1)
Launching soon (papers filed with the SEC):
3. UDN - PowerShares DB US Dollar Index Bearish Fund
UUP - PowerShares DB US Dollar Index Bullish Fund
All of the above track the USDX on NYBOT.