It varies greatly based on type of content. The most I have made was $20k per month on a TV show review site. We had Netflix and Hulu advertising on in through Adsense for awhile and their ads were specific to the individual TV shows we were writing about. The RPM's were amazing.
I also ran a Minecraft mods site for awhile with my son and at its top it made $9k/mo with about 130k unique visitor per month.
More tech content sites or other more general sites I have ran haven't gotten anywhere close to those #'s.
Games and entertainment content geared towards youth do well.
Ad placement also makes a difference. 1 well placed in-content ad can make you a lot more than 3 ads. That one well placed in-content ad can generate a higher CTR and CPC vs. if you place 3 ads. When you place multiple ads, the CTR on all of them even the well placed in-content ad is much lower as well the the CPC. I have tested this extensively.