Rather than list the top 5 by taste preference, I'm going to alter this slightly, and list the 5 beers that have had the most influence in my beer-drinking career, if you can call it that. That may not be the intent of this thread, but I figure it's my list, so I'll design it the way I like.
They are chronological, not preference, order.
#1: Olympia: The first beer I ever tasted, snuck from some leftovers my father had in the fridge. Blech! It tasted horrible to me. I thought I'd never be a beer drinker.
#2: Dinkel Acker CD Pils: During two summers in high school I was fortunate enough to be able to participate in a summer exchange student program, travelling to Stuttgart, Germany -- where the drinking age was 16! Everyone remembers their first love when it comes to girls (or boys). When it comes to beer, Dinkel Acker was my first love. I will always fondly remember this tasty brew.
http://www.brauereigaststaette-dinkelacker.de/index.php?site=Unsere_Biere
#3: Schaefer: Fast forward to my freshman year of college -- my "cheap buzz" period. Almost always had some Schaefer in my little dorm fridge, with the dorm fridge set as close to freezing without actually freezing the beer in an attempt to numb the tastebuds in preparation for this less than stellar tasting brew.
http://en.wikipedia.org/wiki/Schaefer_Beer
#4: Samuel Adams Boston Lager: Everyone on HBT likely knows the proverbial 800 lb. gorilla in the craft brewing space (the gorilla having put on enough muscle that some think it might not be so 'craft' anymore, but that's not the point of this journey). Finally, I'd discovered a decent American beer, available just about everywhere, that I found thoroughly enjoyable.
#5: Murauer. Currently, my favorite commercially produced beer. If you haven't heard of it, don't worry. I'd be pleasantly surprised if anyone has. This one's a Märzen, but not your typical Märzen. This one's brewed in the Austrian Märzen style which is distinct from its German counterpart being lighter in both color and body. Brewed in the Austrian region of Styria, a region known as Austria's "green heart", this is my beer of choice during our family's somewhat frequent trips to Austria - my wife's original homeland. An absolutely delicious beer, it evokes memories of hearty schnitzel and gasthouses, my wife's heritage, winding my way thorough cobblestone streets surrounded by breathtaking cathedrals and churches, and the simple pleasure of spending time with friends and family we haven't seen in a while.
http://www.murauerbier.at
Prost!