DO NOT use any task killers, RAM memory optimizers/boosters, battery savers/repairers, cache cleaners, antivirus, etc etc. None of that stuff is necessary..
Like Rukbat said, such apps are actually counterproductive and some are just plain evil. They actually waste power, disrupt critical system processes and degrade performance. Not to mention the nag ads many throw up.
To understand why such apps are so bad, read the article Rukbat linked. For more - and fun to read - info go back in this thread and read posts # 3, 23, 27, 31, 33 & 180 - especially 180. This thread covers Battery Doctor, which is particularly horrible, and other offensive apps.
http://androidforums.com/index.php?
In short, don't try to micromanage your phone. Don't install software that attempts to either. Let Android handle things as intended. It will automatically optimize operation if you let it.
Don't worry be happy. Relax and enjoy simply using your phone.
Android user since v1.0. Linux user since 2001.