Top three:
Ayinger Brau-Weisse
Young's Double Chocolate Stout
Breckenridge Vanilla Porter
Otherwise, Boddingtons Pub Ale is pretty good too. Buffalo Gold is great for anyone who likes golden/blonde ales. Arrogant Bastard Ale is alright, but a bit too bitter for my tastes, if it was toned down a bit I would absolutely love it.
Killians Red is a pretty good Amber Lager IMO, if I'm in the mood for it.
I enjoy most hefeweizen's as well -- Pyramid Haywire, Hacker-Pshorr, Weihenstephaner. Newcastle Brown Ale is also a good choice at most bars, along with another Brown Ale, Big Sky Moose Drool.
Mostly, I'm a huge fan of Porters and Stouts. Guinness is good but there are many other better choices out there.
Never tried any IPA's, but only because I've only heard of how awful they are.