Bored, so I'm going to talk about my favorite typings!
1. Grass / rock
I love this typing so much. It eliminates the two of the biggest problems with rock type (that being earthquake and water moves) and it's remaining weaknesses are not a humongous concern. It's also immune to all the grass status moves like leech seed and spore and what have you. The only things you have to really watch out for are fighting moves and ice moves, as both bug and steel moves are pretty rare.
Too bad only one single pokemon gets this great combo.
2. Pure water
On paper you might think water types tend to be nothing special with two major weaknesses, and effective against only three types, but you'd be wrong. This is because in real battles, both grass offensive moves and electric offensive moves are quite rare. You wouldn't see more than one pokemon on the enemy team pack them, if they even bothered to begin with. Then you consider than there are a LOOOOOT of walls in the water clan.
Honestly they only have one practical weakness. Toxic.
That or some super powered wall breaker buffed up to his nose with swords dances or something.
3. Poison / dark
4 resistances, immune to psychic, and only weak to ground. It's damn good yo. It's also immune to toxic and will get rid of toxic spikes. Offensively it has access to great STAB moves too, like sucker punch, crunch, knock off, and poison jab. Given how much more useful poison has become, it's a great typing to have. The only thing stopping this typing from being awesome is the fact that only two pokemon get it. They're not too bad but definitely not A+ material.
If a specially defensive wall had it though... holy crap it'd be crazy.
4. Dark / ghost
There's a damn good reason why the only two guys that get this awesome typing have kinda crappy stats. Can you imagine if something with 600 stats had ghost / dark? It's be the most broken shit in the game. Even though it's now (thankfully) weak to fairy, it still doesn't change the fact that it's hard as all hell to kill.
Not to mention those two buggers like to pack will-o-wisp. So good luck ever killing them physically.