Install Fluke and then open up a FLAC file with it (or drag your FLAC files to the icon) and it automatically runs a script that tricks iTunes into adding a FLAC file to the library. For the most part, tagging and even album art will be converted -- though I did have to add track numbers to some of the files I tested. It isn't as seamless as an actual FLAC player, like Cog, but it is certainly more hassle-free than some of the other script-based solutions I've used in the past.
