Android - How can I get rid of the low disk space notification?

Right, I have the solution. Swipe down to get notifications, then hold down on the screen where it says 'insufficient storage'. A little window will appear saying 'app info'. Press that and it will take you to settings of your android system. There is a ticked box saying 'show notifications' Untick that box and the problem is solved. ( the box can be ticked again afterwards, so you can receive other notifications, but the problem should not reoccur).

It is enormously annoying, isn't it? There's no way to suppress it on an unmodified system that I know of, but you can at least free up more internal disk space by emptying system and app caches using an app like SD Maid or by going into the application management section (Settings->Applications->Manage Applications->All, then click on an app name) and manually clearing out app data for hogs like Google Maps and the like using the Clear cache button (note: don't clear the app data! just the cache).

Run these commands from adb shell or a root terminal (the second may not work on later versions of Android):

settings put secure sys_storage_threshold_percentage 5
settings put gservices sys_storage_threshold_percentage 5

The default threshold is 10%, so you can decrease it to 5% or possibly even lower.