One great thing about Michael's is that they have a large selection and the brushes go on sale every month or two. I like the Loew-Cornell white nylons for flat or round. I like the Loew-Cornell 73xx series for detailers, especially the 18/0, but my all-time favorite detailer is the Floquil 20/0 Golden Fox. Tamiya brushes are good, but it's tough to find a store with a large selection.
When you're looking at small brushes especially, the exact number, quality, and arrangement of bristles can vary from brush to brush, so it's important to examine them closely and compare.
Michael's is also good for cheap disposable or semi-disposable brushes.
-Neil