I'd say TIFF is the best too. That's what I use for all my publishing files. It's nice because it lets you keep a very nice image and compress it as well. Other than that, I use the Photoshop format if there are any layers, and the PICT format if I want others to see the image but keep it lossless (uncompressed). And for web stuff, I'd say JPEG or GIF, depending on what it's for....
just my $0.02