Sony, for all sort of reasons (the rootkit and other DRM, pushing proprietary formats like MemoryStick and ATRAC3, removing OtherOS (a.k.a. Linux) support from the Playstation, etc.).
Blizzard, because of Freecraft and BNetD (I was boycotting them long before they merged with Activision).
Ideally, I would boycott Nestle and the other abusive agri-conglomerates, but honestly probably a lot of their products slip through because (a) it’s hard to tell what’s made by who because of all the subsidiary brands, and (b) with all the consolidation, pretty much everything is made by some shitty megacorp these days. I mean yeah, if I eschewed normal chain stores entirely and tried to buy everything from local small businesses or something then I guess I could avoid them, but ain’t nobody got time (or money!) for that.