I can only think of 5. Infernape, Rapidash, Magmar, Houndoom, Flareon. If you have a DS Lite, you can use dongle & get Growlithe & Vulpix. I think in terms of best types to use for a Mono run, maybe Mono Normal or Mono Water.
You'd be lacking HM slaves anyway if you did Mono Grass/ Fire.