But there's so many good styles of beer like strong pale ale, strong dark ale, stout, oatmeal stout, milk/sweet stout, double, triple, quadruple etc etc.
Give me some good names and I'll try to hunt them down sometime!
It kind of depends on where you live and what your local beer stores stock. (Check here to find a beerstore near you
But since I only really have experience with Belgian beers I'll throw down a simple must try list.
Duvel, Strong Pale Ale and the best of its kind. It's fresh, easy to drink, complex enough in taste that it never gets boring and it can hit you quite hard with it's 8.5% ABV.
Westmalle Tripel (Dubbel is good too), the definitive Belgian triple, complex in taste and not something to throw down your throat but a beer that you take a while to drink.
Chimay Grande Reserve (Blue), a brilliant Strong Dark Ale, sweet and malty with some noticeable alcohol.
Rochefort 10, one of the three best quadruples around, complex, lots of alcohol and you drink this more like a wine than a beer. also due to it's 11.3% ABV)
St Bernardus Abt 12, #2 of the best 3 quadruples around and with the third being Westvleteren (which is really hard to get a hold of) these two are going to be as close as you get to beer perfection. I personally prefer the Rochefort 10 but both of these are an absolute delight to drink.
Although I should note that starting with the quadruples is probably not the best idea, they are nothing like a normal beer.
Stouts I am much less familiar with (but working to correct that issue) however I do recommend Anderson Valley Brewing Company's Barney Flats Oatmeal Stout because it's smooth, sweet and rich in flavour and goes amazingly well with some quality chocolate.