Ranged, spellcasting, and other kinds of non-melee monsters

[Kazyan]

My PCs have reached level 13, and during level 12, it became apparent that we had entered the "rocket tag" phase of the game. The only thing the ubercharger didn't instagib nigh-immediately was a homebrew golem with 38 AC, and even then, he got it on his second try.

What sorts of ranged and caster-y monsters are good for mid-high levels? Assume these guys can handle monsters as if their CR were decreased by 3.

[Wacky89]

Flying monsters spring to mind, spells as simple as grease cast at as a ready action infront of him, Prismatic Wall to be super evil, there's ALOT of spells that stops him. If you keep putting them up against stuff on the ground that doesnt do some kind of tactic, this will keep happening.

If u want examples of monsters here are some:

Deathshrieker MM3 p. 33
I'll look for more later

[Kazudo]

It could very well become time to unleash Mindflayers and Beholders on the party. Smart ones with backup, small armies, and fortifications.

Alternatively, there is always Elder Evils.