App to edit apps that start at boot also way to clean temp files

I have some apps that came on the phone and some I downloaded that I rarely use yet I have been told that they come up at reboot and make the phone slower what is the best app to take care of all this I was searching the market but there are alot of different both paid and free programs that make all kinds of promisses. right now I do have the free version of advanced task killer because when I got the phone someone at verizon customer service recomended it.