ACS data by TAZ?

If by TAZ you mean traffic analysis zones i am very much in doubt. You may have to get the data yourself and merge with GIS to aTAZ layer yo created yourself. Having said that, you could try the CTPP : www.fhwa.dot.gov/.../

The CTPP is clearly the way to go; that's the only way to get data by TAZ. Here is a link specifically to it:

ctpp.transportation.org/.../5-Year-Info.aspx

Note that while this is an ACS data set created by Census, its publication and management is in the hands of AASHTO, one of several organizations coordinating transportation planning and statistics. The data were only released about two months ago, after years of planning, coordination, and compromise between Census and the transportation planning community.