ReflectionFest
If you have problems fighting Beholders or those other smaller versions of them (the green ones) then the only thing you need is the Cloak of Mirroring which can be found in the Sahuagin city (I just don't remember where). Equip it with one of your characters and let him be the only one to encounter the Beholder(s), all the spells will be reflected and your character won't be hurt (only the Beholder(s)). Even though there still are spells that won't be reflected (such as hold person) it doesn't matter since your character doesn't have to move anyway and the Beholder(s) do cast dispel magic spells, too. So when they're finished off by there own spells, you collect the xp and you can continue. As easy as it can be.

There's just one minor problem with this strategy... If there are other monsters around you will be in trouble, especially when you're held. That means that this strategy is only adviseable to fighters since they have enough ac and hp's to survive a possible attack.

Submitted by: Bordin Steelaxe

Elementals and Cloudkill
If you have the Cloak of Mirroring or CE Shield of Balduran these are no-brainers. However, they have other weaknesses as well. Gauth's rely heavily on Cause Wounds spells so a Spell Immunity: Necromancy will generally stop them. Aside from that, I have used 2 main ways for dealing with them: Fire elementals and Web/Cloudkill.

Fire elementals can be summoned by a relatively low level druid and since they are immune to most of the beholders spells one of them can usually take out a beholder or 2-3 gauths. Send the elemental ahead of your party and it will automatically attack when it spots and enemy, even if your party can't see it. Just stay out of the way and let it do its thing. Note: Lesser Elementals from mages may work, but it will take a LOT more of them.

Elementals are probably the easiest way of doing it (besides Cloak or Shield), but in my 3rd pass through the game I found myself in the Cult of the Unseeing Eye quest without the ability to summon them. I used the Web/Cloudkill combo that works on almost anything: Send an invisible scout ahead to see where you need to target the spells. Once they are located, fire in 2-3 webs so that the area of the spell includes the targets but keep the caster out of sight. Follow up with 1-2 cloudkills, retreat and wait.

Cloudkill alone will work in many cases, but some monsters will attempt to chase once they get hit with it -- even if they can't actually see you. Web does not trigger them chasing and multiple webs will hold almost any enemy. Web can also work with missle weapons or Free Action spells/items. Kelgorm's Firecam Armor, Arbane's Sword, and the Ring of Free Action are 3 notable ones.

Submitted by: Nighthawk

Short But Sweet
Spell turning baby, spell turning!

They drop like flies from their own Disintegrate and Flesh to Stone.

Submitted by: Vidar

Berserkers and Barbarians
Since the Cloak of Reflection does not provide protection from Hold OR the Imprisonment spell that those Elder Orbs as so fond of throwing at you, there is another simple solution. Get a Berserker or Barbarian. While enraged, they are immune to both of those problems.

Submitted by: Cybot

Glitterdust 'Em
You can cast level 2 spell "Glitterdust." It will blind any beholder group for four round. They can't do anything and you get bonus to hit them (+4). (I suppose the spell level one "Blind" would work but only for one). I've never seen one save vs spell against glitterdust. Now all you need is enough firepower to take them down while blinded. I like this and other ways - the baldurian shield is just too easy. You have to respect those mighty creatures and give them the proper death they deserve!!!

Submitted by: Soloren