Oh gosh - my top five? Let's see: definitely Guerlain and YSL...and I guess I can't forget Dior and Chanel either. But I'm also loving some of the new organic makeup i.e. Josie Maran and Tarte (now that it's been reformulated). I also really like Hauschka makeup - so pure and such high quality.
Then it gets into category-specific stuff eg. Lancome for mascaras, NARS blush... etc etc. I could go on and on so I'll stop now. So hard to narrow it down!