When I have travelled, I generally don't go about trying to snap the ugliest buildings possible, but here are a few nonetheless. I don't pretend these buildings are the world's ugliest by any means, but they are unpleasant in various ways.
Tel Aviv is a great city with some fabulous buildings, but no small number of really hideous things as well. The post-modern whatever it is on the waterfront, in my opinion, is so chaotic that it beats anything in Toronto hands down. I don't even hate it exactly, it's more like a joke than anything else.
These two monstrosities are among the tallest buildings in San Diego, and you can only pity them for it. It's not just that they are pretentious and ugly, but they're so very prominent in the downtown.
With this collection of apartment blocks in Seoul, the probably is not so much the banality of the individual buildings, but their endless repetition in an array that seems truly suburban. This photo is taken from one of the tallest buildings in the city.
Hong Kong was a surprise to me in that so many of its residential buildings, which collectively look dense and incredible against the mountains, are quite ugly close up. Massive blocks with their plumbing and utilities running up and down the outside of the building, even on very recently built structures, they make you weep to consider them. This one has maintenance problems to boot.
This massive abandoned structure on the right (part of two apartment buildings glued together) near the market in central Sao Paulo must have been sort of ugly even when built - each floor is marked by three horizontal concrete bands that really make it seem larger than it is. Currently, it's abandoned and covered in graffitti, which isn't helping any.
Istanbul's modern buildings have a distinctive style that I can only call "butch". They seem excessively concerned with being masculine in some way - so many of them felt heavy and cumbersome to me. I could have picked any example, but this one is particularly bad because it's relatively closer in to the historic part of the city, and because it is the only tall building in its neighbourhood, it is very prominent.