I wouldn't ban anything but legendary Pokemon, everything is beatable. Banning moves is the most rediculous thing I've ever heard of!
Well, everyone is entitled to their opinion. I think that you're wrong in that aspect, but that's just me. As for my usual personal rules, I use all the same ones that Marril uses (thank you Vaporeon for that quote), with the addition of a Legendary ban, as I like to see some interesting teams that use a variety of different pokemon. I also prefer the non-use of moves such as Double Team, for the reasons stated before as well as this new one that occurred to me last night:
Moves such as Screech or Agility are very usefull attacks, as they give you the added benefit of additional power. The price, however, is that your opponent essentially gets a free shot at you. Defense and Special Defense raising moves or Attack/Special Attack lowering moves have an additional benefit of weakening the attack if that pokemon happens to be faster, but the pokemon still takes damage. However, accuracy and evasion altering moves such as Double Team and Sand Attack not only alter stats, changing the effect of attacks in the long run, but if used by a faster pokemon, an evasion raising/accuracy lowering move takes away that negative side effect, giving you a powerful effect with no negative side effects. It's the same reason that there is no attack like thunder Wave for freezing, and why Sing is so inaccurate. Sleep and Freeze are powerful effects, but you can't just use them directly without risking negative side effects (Sing misses, wasted turn).
That has become my main arguing point against DT, as well as other evasion raising and accuracy lowering moves like Sand Attack. However, Evasion lowering and accuracy raising moves are no problem, as they do not infringe upon this rule. So, my regular rules are:
Species Clause
Item Clause
Suicide Clause (my personal name for it)
Sleep Clause (I don't have a Freeze Clause as Freeze is not an actively controllable effect)
Legendary Clause (Wobbuffet included)
Accuracy Lowering/Evasion Raising Clause (Inactive effects such as that of Muddy Water not counted)
Edit: Vaporeon, those of us who ban Legendaries ban them because we dislike facing the same pokemon over and over. It's more interesting to battle different 6-Pokemon combinations of 454 pokemon as opposed to combinations of 39 Pokemon. Thats all. I'd even go so far as to allow one Legendary in your team, as long as the rest are creative.