The Eldrich Master PrC from Dragon 280 is similar to the rainbow savant in that it grants access to another spell list. It grants no spell casting progression, but at level 3 (every 3) it gives you a spell slot one level higher than you can cast and at level 4 (every 4) grants you access to another classes spell list. Note, it does not add this spells to just one class, it just lets you pick up spells from the list regardless of what classes you are taking. Also all of these spells are cast as arcane spells, so
Beguiler 16/ Eldrich Master 4: Beguiler spells + one other list. 9th level max.
Same as above for Warmage and Dreadnecro (and you can still prestige)
Savage Bard 4/1 x/Ur-priest 2/Eldrich master 4/Mystic Theurge 4: All Cleric + one other list. 9th level max
Note, I think it is funny to double advance Ur-priest with mystic theurge since it is now a divine and arcane spell caster. If you go this route, you can take another 4 levels of Eldrich master to pick up a 10th level spell slot at level 6 and another spell list at level 8.
An archvist is better, but these builds dont need books, and the first one does not even need to prepare spells. My favorite though, but not all knowing is:
Bard 4/ Cleric 1/ Eldrich Master 4/ Dweomerkeeper 1/ Sublime Chord 1/ Dweomerkeeper 9
You can cast from the Bard/Sorc/Cleric (thanks to Eldrich Master) from your sublime chord levels. Plus is is divine metamagic ready (alternative sourced spell), supernatural spells are go, and allows you to pick up Miracle as one of your 9th level spells to copy just about everything you might be missing.