I think the best building, or the building i make the most often, is the Temple.

Its easy to make (only 40 resources) and culture is in every city unlike gold and science

The best wonder is colosses, at a cheap 100 resources, (50 if rome) doubling trade, its a early great wonder to have

Well, depends of which era are you in. Bank, Temple, courthouse, all of them awesome buildings. As I said, all depends of you game style and era.

East India Company which adds a very nice bonus to trade squares and the obvious very, very overpowered Leonardo's workshop. I've never built it, but the Apollo Program seems like a sweet wonder when you're behind

Colossus, Library, University are all great. What can I say, I'm a science-holic!

Barracks, baby!

Woohoo warlords!

barracks gets my vote too :P

ive won several games building nothing more than new cities, military units and barracks!

Courthouse is great, while also is a library, university, and cathedral. The point is, a balanced good city should have a bit of everything. One of my favorite wonders will be the Manhattan Project, obviously. I also enjoy the hanging gardens, pop it into your main city and BAM! 1.5 your population, that greatly helps if you are producing a mega city!