Alright. Well, Johto Pokemon are kinda scarce, so let's see:
(no particular order again)
Smeargle - This guy seems like an oddity. Low base stats, and knows only one move. So, why? It's because the only move it knows, Sketch, allows Smeargle to permanently copy the move of any Pokemon, allowing its moveset to be virtually unlimited bar two moves: Sketch and Chatter, and who cares about Chatter?
Jumpluff - Speed + status moves = supporter. This cute Pokemon can lay down powders and Leech Seeds at blazing speeds. In addition, knowing Sunny Day turns Jumpluff into 1) a very effective Sunny Day team member and 2) making Jumpluff one of the fastest Pokemon in the game. Sad that attacking stats are mediocre.
Miltank - Stats seem geared towards either attacker or wall. And Miltank can do both, with appropriate moves for either purpose. In addition, 100 base Speed. Awesome. And Scrappy. Very, very good.
Wobbuffet - There is a reason why this Pokemon and its baby form, the BABY form, mind you, were banished to the Ubers tier. Actually, several reasons. How about these: Counter, Mirror Coat, Encore, and Shadow Tag? With obnoxious HP, Wobbuffet can absorb virtually any blow and Counter/Mirror Coat it. Encore can be used to made prediction much easier. And with Shadow Tag, the opponent isn't leaving any time soon.
Kingdra - Use Rain Dance. Watch Kingdra sweep through team. Success.
Notable mentions:
Skarmory - I used this guy in Hoenn, but Skarmory is known for being one of the best defensive walls, with Steel-typing and high Defense. Really, though, Skarmory can be used as a suitable attacker, as well.
Octillery - Uh...yeah. Octillery is kinda odd, with a large movepool and Suction Cups, of all things. This makes it useful for Baton Pass teams, but I never really liked those.
Houndoom - Special sweeper. Look at that high Sp. Atk and Speed. OK, maybe the Dark and Fire-typing may not be so good, but with Houndoom's fantastic offensive stats, not a lot of things will be left standing.