Play with a metronome. This REALLY improves timing.
A metronome is very unforgiving. If you play without a metronome, you will inadvertently speed up or slow down when playing lines you find difficult or challenging. A metronome won't let you do this. It will force you to stick to the rhythm. If you haven't played with a metronome before, you might hate it at first! :) However, it will really improve your sense of rhythm and timing.
Whenever you are playing a song or a scale, play it with a metronome. After playing along with the metronome for a while, switch it off and try playing without it. You will be able to feel the metronome's rhythm even when it is off.
Here's an online metronome you can use:
Korg also makes some really nice Metronomes.