Rubbing alcohol is also my primary thinner for acrylics. I use it with Model Master, Tamiya, and Citadel with excellent results. Two things to keep in mind though:
1) It evaporates quickly and tends to make the fast-drying problem of acrylics even worse. I usually add a couple of drops of acrylic retarder to my paint cup to slow the drying time down.
2) With most Tamiya gloss paints it will cause them to dry flat.
Other than that it works great. You can also use automotive windshield washer fluid. I haven't tried that but I understand it works quite well.