There are many of them in the Market. Some are single function. Currently I use 2 multi-function apps which has torch:
1. Swiss army knife (free): there is touch which light up both camera led and/or screen. And it has some other useful tools. The other free app called "Super swizz army knife" doesn't have a proper torch but has better other tools.
2. Widgetsoid2.x (free): excellent app, which provides highly configurable widgets. I put two button bars of its on the home screen with a lot of on/off button for all kind of on/off things like wifi, data, bluetooth... and flash (torch) of cause. For torch - please select method-2 in advance configuration page, otherwise the camera led won't light up.
You can also try the app named "Torch" in the market with a home screen widget providing nothing else but torch on/off button.