If you have access to dragon magazine, issue #280 has the eldrich master PrC class. This class allows you to add another classes spell list to yours every 4 levels. It also nets you bonus metamagic feats and a bonus spell slot one level higher than you can currently cast every 3 levels. Finally it adds its level to all level based effects of a spell cast by an arcane caster. So for instance if you were a wizard 5/ Eldrich Master 5 casting a spell, the duration, range, and damage would all equal to level 10. It does not actually increase your caster level though (so spell resistence checks the same).
Black Ethergaunt 20// wizard 1/Saint Template 2/Monk 2 (if you want Int to AC)/Eldrich Master 10/Geometer 2/Uncanny Trickster 3
What do you get
1) Full 20 levels of Spell progression with effective caster level of 32 before equipment
2) Wizard, Cleric, Bard, and Druid Spell lists
3) Dex, Int, Wis to AC
4) Outsider type
5) One page spells in spell books (Get Baccobs blessed book, your spell book will basically be the entire Spell compendium)
6) 4 bonus metamagic feats with only 1 feat required for build (if monk, Int to AC)
The order of the build can be moved around. Have the wizard offest the 1 LA in the first 5 levels and the 2 geometer levels offset the remaining 2 LA for full casting progression. The monk levels are not needed, but as suggest by woodenbandman they can give you Int to AC. Also the saint template gives you the outsider type and wisdom to ac as suggested by anomalousman.
The only trick here is using the Uncanny Trickster. Using it to advance Eldrich master above 10th level Pre-epic maynot be allowed by some DM's. You can always drop it and still have 2 extra spell lists and 3 bonus metamagic feats.
I have a similar gestalt build Beguiler 20//Cleric 2/Bard 3/Eldrich Master 5 (cleric list to beguiler)/Sublime Chord 2 (selecting beguiler for spell caster level)/Dweomerkeeper 8 (advancing sublime chord). Ends up with a caster level of 30/ 35 effective. The beguiler can spontanously cast its list plus the clerics, while the sublime chord has Sorc + Bard spells. The races of destiny's Illurien (spelling) race used to give effective divine metamagic persistent spell with any list, not to mention no component casting from dweomerkeeper.
Sorry for the long response.