Wizards can learn spells from spell books, scrolls, and the spell Blood Transcription, but are there additional ways for them to learn spells?
They can invent new spells with the GM's permission.
As they go up levels they gain a couple spells each level automatically; some of the favored class bonuses add another.
If you add 3.5 material in, there's a Magical Location that grants a wizard a new spell known. I believe it's in Complete Mage and has Boccob in its title.
In 3.5 you can also acquire feats and associate with certain organizational Affiliations that will give bonus spells known per level.