Beholders are really the most difficult for me to fight. They feeblemind me before I can even hit them (even around corners), which reduces your average spellcaster to throwing rocks.
I'm a PM so neg levels and whatnot aren't a huge issue. The biggest thing I have to worry about - with the exception of the feeblemind - is disintigrates. Yeah, taking them out from a distance is a decent plan solo, but I usually PUG, and PUGs usually don't take their time with handling these guys. So I end up being in the thick of battle, feebleminded, and not really able to do much.
I have the Ioun stone that absorbs charges, but it appears that this does not absorb feebleminds. I haven't experimented enough to tell for sure.
I'd appreciate any pointers about dealing with beholders as it comes to spellcasting. Is there any way to avoid the feeblemind, or is hitting them first from a distance my only real option?