Parian Spirit Professional more...
This product works great at cleaning the brushes I use for liquid makeup products, like foundation, BB cream, and lip stains--I have another product that I use for the powder-based products (Bare Escentuals brush conditioner). I spray a few pumps of the product on the brush, let it soak in a bit, then start moving the brush in circles on a stack of paper towels. The leftover product residue comes right off onto the towel. Repeat as necessary then leave out to dry. Result = good as new, without a trace of old foundation or eyeshadow residue.
The only downside of this product is the smell. It's heavily citrus-y, and honestly, I'm not a fan. But the product does such a good job that I can deal with the slightly chemical orange scent once in a while.