as most of you know, there are different types of battles, i think i'd be appropriate if we had them all listed:
Standard Battle:
the rules by witch probably 90% of battles are done, we've posted these rules multiple times on the site so i'll link it to ZDingen's post on it
link
if both players agree different clauses can be turned off and on, it can be played at lv. 50 or open, and can be played from 1-6 pokes, ect.

Roulette Battle:
from my experience one of the more popular styles of battling when not playing a standard battle, Drew posted these rules, so i'll just link it to his rules
link

Mono-Type Battle:
the rules that our gym leaders and elite four play with, it's basicly the same as a standard battle, same clauses, just that your team must consist pokemon of the same type, like if you chose fire type you could make Houndoom, Infernape, Heatran, Magmotar, Charizard, and Macargo or something like that, if both players agree you can add in a filler or a wild card poke, witch is any poke not of the type, like replacing Electivire for Infernape to the fire team, you can use as many fillers as you both choose

Mono-Color Battle:
yet again, whatever of the standard clauses you put on, except your team must be all of one particular color, like if i made a blue team i could use Vaporeon, Salamace, Swellow, Toxicroak, Garchomp(eh...i'll add an uber here, lol) and Shiny Porygon-Z, most people play it by eye and as little as 1/3 of the poke should be the color, like adding Swellow or Ryperior to a red team, or you can play with the pokedex colors in the link below, if you need one or two you can add a filler or a wild card who isn't of the color
http://bulbapedia.bulbagarden.net/wiki/List_of_Pokémon_by_color

Rainbow Battle:
if i recall Slowfreak either invented this or first showed it to me, it's a spin off of the mono-color battle, basicly you both lead with a red pokemon, then you need an orange, yellow, green, blue, and purple pokemon, because the pokedex colors don't include orange, you can either switch orange with brown or play the pokes colors by eye

Mexican Battle:
1) All of the standard clauses, including no Ubers
2) No legends
3) Only one "titan", which is the following: Gyarados, Metagross, Tyranitar, Slaking, Salamence, Scizor and Dragonite

Tier Battle:
both players agree on the clauses and what not, the difference here is that all six of your pokemon must of the same tier(uber, OU, BL, UU, NU, or NFE), tier list is in the link below, so like an Uber team could be Kyogre, Deoxys, Manaphy, Garchomp, Wobafeet, and Palkia, or something like that
link
(thanks Alex for reminding me on this battle type)

keep us updated on different types of battles, lets see if we can list them all =)

Monkey

Mexican battle??

Hell yeah!
Mexican Battle:
1) All of the standard clauses, including no Ubers
2) No legends
3) Only one "titan", which is the following: Gyarados, Metagross, Tyranitar, Slaking, Salamence, Scizor and Dragonite

My kind . Where's Uber and UU?