Watchdog will monitor your phone's performance and alert you of issues. Here's a quote from the Lifehacker article on Watchdog.
Watchdog runs in the background,
watching for apps to start using more
than a certain percentage of CPU power
that you specify (with a default of 80
percent). When it notices an app going
out of bounds, it notifies you and
offers options to kill the app, ignore
it, or add it to your "Whitelist" of
pay-no-mind programs. By default,
Watchdog doesn't use much power
itself, only checking in every two
minutes or so, but you can make it run
more real-time if you'd like to really
pin down a problem you know is
happening.
