Pokemon White Team Building Help

Alright guys, so I have a small problem. I'm at Icirrus City right now in Pokemon White, and I only have 3 Pokemon that I keep with me to battle. I have:

Sigilyph @ Lucky Egg
Gentle, Level 42
Psybeam
Air Slash
Fly (I know, it's bad.)
Thunder Wave

Scrafty @ Expert Belt
Jolly, Level 42
Crunch
Brick Break
Hi Jump Kick
Strength

Lampent @ Amulet Coin
Naive, Level 42
Flame Burst
Toxic
Hex
Inferno

Ok so when I first got these pokemon I paid no attention to their natures, and that was my mistake. I might have to go back and fix them, but so far they've done what I need them to do, so I won't worry about it quite yet. My problem right now is that I need to fill 3 more slots and I'm already pretty far along in the game. My priorities are Grass, Water, Ground, and Electric type pokemon.

For the grass type, I was planning to get an Adamant Simisage with Crunch, Seed Bomb, Rock Slide, and Toxic. This might work or it might not, but that's my plan for right now. If anyone has better ideas I'd be glad to take them into consideration.

For the ground and water type I might use a Seismitoad but it would have to have a neutral nature, like quirky, because I would be using both physical and special attacks, like Earthquake and Surf. It would probably work but I don't love the idea of a well-rounded pokemon. I prefer extreme pokemon that have one or two super high stats instead of an all around decent pokemon. I know that sometimes this can be dangerous but it usually works out well for me.

So now this leaves the electric type, which does bother me a little bit, because there aren't really any amazing ones in Black and White. Zebstrika is out of the question completely. I don't like anything about it except the speed, which is not really enough to make me want one. So now there are a few left that I can think of. Tynamo, Galvantula, and Stunfisk. So out of these I would choose Tynamo because even though I prefer the special electric moves, I love the fact that he isn't hurt by ground. So if I got Tynamo, I'm not sure what the nature would be, but I would evolve him to an Eelektross as soon as he evolved into an Eelektrik, just because his special attack would grow faster and almost at the same rate as his attack. I already picked up the Thunderbolt TM so I would be able to teach him that one immediately and put him into battle. I don't really love Stunfisk but if anyone can give me a good reason to get one, then I'd be glad to try it.

Thanks guys!
- Cam

Your current team's nature are okay because none of them touches their main stats. Your movesets are good also. For a grass type, Simisage can work but you also have an option to Own Tempo Lilligant with Quiver Dance/Petal Dance/Synthesis/Hidden Power(a good type). For water or ground type, don't use Seisimitoad. I have used it before and I had a pretty bad experience with it. You could use a Swanna to get rid of Fly on Sigilyph and use Fly on it instead. And for your electric type, I highly reccomend Galvantula or Electross. Galvantula can use Bug Buzz and Compound eyes boosted Thunder and Electross can use Wild Charge and Crunch. But Tynamo is a bit hard to train so you are better off using Galvantula.