Products or services - try to keep it relevant to the viewers of this site in some way. If things get crazy I'm sure we can hold a community discussion about it and find out what ads people want to disallow.
Products and services seems to restrict things like Team recruiting ads (which are also something I'm glad to see, and may be interested in posting some time).
Getting more exposure for help wanted posts for good indie teams could be a big motivator in getting the GDNet+ and joining the ad circulation.
Can we nail down a broader range of advertising subject matter?
I would want to say, anything game, software, or gamedev related, but keep it PG-13.