In the world of computing, the only company really worth hating is Adobe.
Do you mind saying why? If it's the pricing, you have no reason to single them out. For the price of certain other pieces of professional-grade software, such as Maya, Avid and Wolfram Mathematica, you cam buy the whole CS5 Master Collection.
If it's Flash, then you have a partial argument. However, rather than hating Adobe, your energy would be better spent telling the FOSStards at Firefox, Chrome and Opera to allow users to use their h.264 codecs; at the moment, there's no viable alternative to Flash.
The only really rageworthy thing they do is try to sneak a trial copy of McAfee in with their downloads. Cunts.
EDIT: wow, the forum censors mild swear words but doesn't censor that?
A few reasons. First, their software is massively bloated, often for stupid reasons (they can't use system-native GUI tools for example, they make their own instead). Secondly, the price (specifically of Flash). It used to be affordable for home users, but literally as soon as Adobe bought Macromedia, they raised the price just because they could, before they even had a new version out with any added features. It was a dick move, and a slap in the face of consumers. It just so happens that there was a huge drop in things like flash games and cartoons on newgrounds about when this happened, and that was certainly no coincidence. They're basically charging a "you have no other choice" premium, and that genuinely pisses me off.
And then there's their insistence on pushing pdf as a web format. NO IT FUCKING ISN'T, IT WAS DESIGNED FOR PRINTING, IT SUCKS FOR EVERYTHING ELSE. Adobe Reader, in spite of having very little it needs to do, manages to be far more bloated and resource sucking than most of their high-end creation software, nag for updates for every language in the world on a near-daily basis, and really has no business being used anyway.
I think as a whole, my problem with Adobe is their attitude. They spit in the face of consumers, but since they control a number of industry standards, everybody else has no option but to take it.