Switcher a freeware task swicther popular on the Nokia 92x0 is now available on Series 60 (for the 7650 and 3650). A new version 1.4 has also been made available which improves installation on the Series 60 devices.

Task-Switcher will let you:

list your running applications
tell you how big they are in terms of memory usage
close applications
switch to an application even if it is not a graphical one

http://www.ki-ag.de/html/tech/nokiaswitcher.html