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Good question! I´m in the process of converting my game to 3.5 from 3.0 and I´ve no idea.
I don´t have the search function, but I know there was a huge thread on EnWorld that dealt with all the changes between the books.
It seems that they just removed the skill, but why? I don´t know.
Concentration would also seem a viable skill choice although most of the suggestions so far would be maxed out anyway for most wizards. I don't see any problem in just rechoosing the skill points.