Tilesetpal is definitely a great choice, since the way it optimizes palletes means you can draw something with more than 256 colours and it will still look good after you run it through that program. Not AS good, but still better than what you'd normally get. Still, its best to limit the amount of colours you use. Note that because the sprite pallete is part of the tileset pallete, you really only get 174 unique colours to work with, and if you use a textured BG then you have even less space.