[3.5] Yet Another Beholder Topic - Beholder-fighting Tactics Useless?

[Lord Vukodlak]

I once had my fighter leap off a tower, grab onto a beholder with a grapple and force it to the ground. I was far stronger then the beholder giving me the grapple advantage despite its larger size.
The beholder could not stay a float with 300lbs of reptilian fighter clinging to him

Personally I say putting the 90° degree arc line between the party members is cheating where ever the first eye ray fires should be the center of the 90° degree arc, as is any of that move nonsense, That limitation was created for reason and is part of his CR.
If you can make a 90° arc at any point that had more then 3 eye rays shot through it, its cheating.

A few things that can help, darkness, mirror image, displacement, anything that gives concealment or an outright miss chance. Greater Invisibility would work well to.

If the DM is going to use the best cheese he can when facing a beholder do the same in return.

Here is one way to fight a beholder, cast ray deflection. The spell makes you immune to all ranged touch attacks, including ray spells and ray attacks made by creatures. ANY ray directed at you is automatically reflected harmlessly away.
Spell Compendium page 166
The problem its range is personal and its a 4th level spell so no potions.

However for that wizard or bard he is immune to any direct assault laid upon him by the beholder as his ray assaults bounce away. Which means you only need worry about telekinesis, but some displacement+mirror image can buy time with that.

From there I'd advise something simple like Flesh to Stone it has the range and would be instant death on a failed save, stuff like stinking cloud also works.

Other tactics include the Dimension door drop, the caster may be unable to take more actions the same can not be said for those he brought along. Dimension door your biggest strongest friend directly over the beholder with say a Protection vs alignment up and maybe an enlarge person for extra weight and grapple bonus.
Bring the beholder to the ground and you can just move in.