I use a scuba cylinder with a tyre inflator attachment. One quick burst and all the dust is gone.

I was thinking along those lines, trouble is I don't have a scuba tank.

My idea was to get some kind of tank that I can pressure up using a foot pump I have. I definitely think that blow is better than suck in this case.

I have been using the brush and vacuum suck principle but could never get in to the tricky bits especially the CPU heatsink, and while those expensive cans of compressed air have their use they are pretty weak, a strong blast of air will clean out the computer in seconds.

The best brush is a clean, dry, soft toothbrush. Paint and makeup brushes shed and break on the motherboard, and such, rough spots. Just be careful not to use too much force as you don't want to bend anything.

While the case is open be sure to re-seat all your add-on cards and RAM. Also, once it a while, cleaning their contact points with an eraser removes the tarnished buildup that can cause your card to malfunction, short and overheat.

And the vacuum is definitely the way to go. Suck not blow! Blowing will fill your unused slots with dust that may render them useless in the future.