Phil coffee shop near the MQ is ideal
Starbucks, if you are not offended by visiting this American icon in the city of Sacher... :-)
Ibis Hotel in Lassallestreet offers free WLAN.
Check http://www.freewave.at I was using their wifi at Café Sperl on Gumpendorfer Straße. They have hotspots all over Austria by the look of things.
Cafe Prueckel http://www.prueckel.at/
Cafe Englaender http://members.chello.at/englaender/default2.html
the best list of free wlans in vienna (plus 183 locations in austria) is here:
and you can get free internet access @ all austrian mcdoald's restaurants