0x7d3ae940eb73dc9131758ad2e326c7d863b0916a
Honest failsafe Ethereum doubler. Works on both ETH and ETC chains.
Fee is as low as 2.5%. No deposit minimum/maximum limits.
Source code verified:
http://etherscan.io/address/0x7d3ae940eb73dc9131758ad2e326c7d863b0916a#code
https://live.ether.camp/account/7d3ae940eb73dc9131758ad2e326c7d863b0916a/contract
Recommended gas: 200000
Just send ether and wait for profit. All sent ether will be returned if an error occurs.