These sites will also give you advice on training your Pokémon, or offer strategies and other things. Note that the Links section is where you can find information on Pokémon in general.
Kmoro's Pocket Monsters - this site is based on the Japanese version of Pokémon, but it offers a little help on training Pokémon as well.
PikaPower - has a TM/HM List and a Battle chart. I might add that the battle chart looks strikingly similar to Pokéland's battle chart, though. Hmm.
Pikachu's Pokémon Centre - almost too much stuff! The info section has a TM/HM list, Game Shark codes, info on the gym leaders, and more! My only complaint is that it is on Geocities, which exploits their members sites with advertisements.
The Pokédex - this site also has a Pokédex, plus a walkthru, and codes. Also, there are GameBoy emulatoins of Pokémon if you want to scam Nintendo , Creatures, and Gamefreak. Please don't download it.
XKP's Pokémon Page - Pokédex, TM/HM List, Walkthroughs and Cheats.