I'm completely replying upon folks like TBN to define (and argue about) the exact definition of "Mass-Marketed, Widley Available" beer but I'm talking about beer that is widely available internationally and really too large for me to consider a microbrewery.
In my mind the likes of Leffe, Budwar, & Fullers are the size that we're talking about.
I have to begrudgingly nominate Leffe Vielle Cuvee; I'm almost certain I've had it before but this is the first time that I really appreciated it; had 2 while watching the Barcelona vs. Arsenal game this evening and it is really good for being so mass-produced; I wish I could find it in all the places I can find the Bruin...
Budwar has to also make my list; one of the best for its size and cost; especially for a lager.
Adam