Not saying there are not any more, but thats only one I know of..their software is actually pretty damn nice.
Includes a full API too. My only grief with them is when I applied to open an account it took fricking ages for them to get back to me so I ended up with someone else.
Cybertrader has trailing alerts and can be based on bid, ask, or trade price. In order not to get jerked out of a trade by a bad tick, I always use bid and trade price for long stops and ask and trade price for short stops.
Yup - GFT does offer this although only in their new release version 2.0 of DealbookFX - this is still in beta phase although I believe they are preparing to move across certain live customers.