Most of signal providers are just scams that show up for a while and then go. The only exception i know is fxmaster.net. They have been around since 2004. But even this one needs very careful money management and a quiet big accounts since they have big draw-downs from time to time. However...
They send medium term trades. All signals are limit orders that may take hours or even one day until the open. The average duration of a trade is around 1 day. Some trades close in few hours and other trades may stay open 2-3 days. While a trade is open on one currency, they don't open any new...
Learn to do the technical analysis yourself and use a signal service as secondary help to support your own view of the market.
A good signal service i use since 2005 is www.fxmaster.net
You can read reviews about it here http://www.forexpeacearmy.com/public/review/www.fxmaster.net