Verdict is out on task killers (my brother has a Droid and has had a task killer on it for an entire year with killer battery life) but the general consensus is that they're pointless or bad. At first the battery life does seem terrible, but there are a lot of little things you can do to save battery life.
1. Root - but that is the most drastic measure. I, and lots of people here, would recommend doing this to use your phone in its fullest potential. But it can look a little scary to someone who isn't very techy (like me). If you read the forums about rooting your devices and feel up to trying, I recommend it.
2. WiFi - Turn this off when you can't connect to WiFi. It drains the battery searching for networks if you aren't connected to one.
3. Brightness - Put your brightness on Auto or just on a very low setting. Display is the main culprit for battery drain.
4. Auto Sync - If you have this on at really short intervals, this also drains battery.
There are tons of other things you can do. Search the forums. There are lots of threads about battery life! Welcome!