I find that some well known companies in Java world (Jetbrains, Zeroturnaround) advertise quite a lot on SO. I already have their products (both of them actually), so this advertisement is a waste for me and them too. Would be nice if I could disable the ads from specific companies. I don't want to downvote the ad, because it feels as if I didn't like the product, which is not the case (quite the opposite actually).
The downvote module that appears when you hover over an ad can act as a solution to your problem:
For your situation I'd say 'Other' applies.
While I acknowledge that this does not disable all ads for a particular advertiser or product, it allows you to control which ads you see. I think blocking all ads from Advertiser X is not the best solution. Consider the possibility that an advertiser like ZT or JetBrains, whose current products you already use, releases an update or a new product and chooses to promote it by advertising on SO. You may benefit from still seeing ZT or JetBrains ads.
Alllllll that said: we hear you. As stated above, I think the downvote module should work for your use-case. Let me know if you have any additional feedback, though.
As a reminder, relevant blog about the voting module here.