Is there an app I can download that will kill (or quit) other running apps?

Not that I'm aware of. This isn't Windows Mobile, so there's no real need to kill an app.

i need to kill My Verizon because I open it and forget that sometimes it wont close it just stops at "Thank you for using my Verizon" so it stays open until I do a battery pull. But that takes too long

generally any app can be closed by using the menu key. Have you tried it?