Hmmmm... This is a bit tricky. I don't like a lot of publishers, so it's really hard to narrow it down to one. Instead, I'll list three. Also, this list is more of a "What have you done for me lately", except Sega. In my book, Sega gets a free pass due to the Dreamcast being so amazing.
1. Nintendo
I have not enjoyed Nintendo since the N64 days, and now with the Wii, they seem to be more interested in stock piling their system with expensive shovelware games that take advantage of clueless parents and the elderly. They rehash the same IPs over and over again for their "big projects" and produce crap the rest of the time. Hell, most of their crap is filled with recognizable IPs and are leaching off the weak and misinformed.
2. Activision Blizzard
I am currently on a boycott against Activision Blizzard that started after the purchase of Prototype. Although I know it is pointless (I don't care), but I refuse to let them see one dime from me. Their evil is well known and it is unnecessary to go over the many reasons. With that aside, their games have no appeal to me. Activision continues to put out hurried up slop that seem to get worse and worse in quality. Their business is catered to a wretched fan base that stereotypes what is wrong with gaming i.e. old xbox commercials. As far as Blizzard is concerned, I never have and never will be interested in their games.
3. Zynga
No explanation needed.