I can play with this for much longer than I should

[bobthedinosaur]

http://grantkot.com/MPM/Liquid.html

[Machete234]

I try to make it behave liek water but I can just get oil

[Karl]

The HD Flow demo looks quite impressive
it is just bad that i cant run that offline wich is stupid imo

Edit: unrealated but i think it fits to wich is very fun is
OE-Cake
You can even mix stuff with it! (use hotkeys for that)
google for it