...Aaand here come the Upper_Krust acolytes to the fray. Honestly, how long could it be before one of us showed up in a thread like this? This time I'll be the one to bite.
Lacking high-CR monsters? Check out the
Epic Bestiary Volume I for critters ranging from CR 6 (Diamond Guardian) all the way up to the stratospheric, all-but-incomprehensible CR 9721 Neutronium Golem (though in recent posts in the Eternity Publishing forum Upper_Krust suggests that this number needs revision down to "only" 1100 or so). In between you'll find remnants of the original inhabitants of Hell, several new Abominations to frighten Epic characters with, an extension of Dire creature rules so you can inflate beasts to city-size and beyond, mighty dragons born with the universe itself and woven into its very fabric, and more ideas and supplemental rules to help a high-level game than any book I've seen since the ELH itself. It's got Epic items, including artifacts, new Epic feats, a new special material, and rules to extend the game's existing size rules to infinity if you want critters that big.
There's a reason a whole
section of the d20 NPC Wiki is using the rules and ideas from this book, folks.

Seriously, check it out. I've used several creatures from this book in my Epic game (currently at 28th level) already, and been very satisfied with the results. Also, those in the Creature Catalog forums may have seen a little beast called the
Mortiverse, which is largely based on the Immortal's Handbook rules and ideas.
Now, it is true that a few things in the Bestiary refer to books U_K's writing which aren't done yet, most notably Ascension which will contain complete rules for statting up gods, servants of gods, Overgods, and even beings beyond the oVergods. He is, however, working on that now, and scuttlebutt is that Mongoose Publishing's new Flaming Cobra imprint will be publishing a print version of the Immortal's Handbook series sooner or later (though there apparently isn't an actual scheduled release date for Epic Bestiary Volume I, the first in the series, as yet). Other books in PDF form will presumably be published under the same imprint as time and publishing vagaries permit.