Best tech support forum for Microsoft Office?

MSDN would be the first choice.

For Microsoft Excel, there are many. Following are few popular ones.
http://www.mrexcel.com/
http://www.ozgrid.com/
http://excel.tips.net/
http://www.cpearson.com (Chip Pearson)
http://www.andypope.info/ (Andy Pope)
http://www.experts-exchange.com/

Whenever I get a problem, I use to search on google, so it throws up related results quick.

Did you try going to Microsoft.com? They provide pretty extensive and robust support for their office suite. I’ve definitely found their support useful.

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