I have an HTC Incredible, but here is what worked for me.
Settings -> applications -> manage applications -> all
Click: menu -> sort by size
This shows the memory hogs! Now go into the top application and do the following...
Click: Data -> Move to SD card
(or you can clear the data if you want)
The notification then removed itself from my tray. All better. Netflix was doing this to me. Repeat steps for other apps as needed.