Look on the market for "ATK", it's free.
However, what was likely sucking your battery is you having GPS on while doing so. Android is designed to multitask, and using programs to actually kill tasks is quite debatable. It's actually possible that actively killing tasks with a seperate app uses more battery than letting Android handle it.
By far the most battery is used by the screen, GPS and Wifi, so keep an eye on those before anything.
And on a new phone, charge the battery full, then use it until it's empty (without charging in between). It's generally best to only charge it from near empty to full. Actually this bit used to be true, not so sure about modern batteries, but it can't hurt and feels cleaner tbh.
Other app recommendations:
- Launcherpro Plus
- Beautiful Widgets
- Trillian Beta
- Act1 video player
- Locale
- Navigon
- Pure calendar widget
- Setcpu
- Touiteur