Are there any domains that I should definitely block in my personal computer's etc/hosts file? I'm thinking of domains that provide no service to ME but are just used to track/target advertising/etc.
...And spend your life managing hosts? If this is only for your browser install uBlock and add whatever filters you're interested in. You can also go one step further and disable JavaScript, only re-enabling it for sites you care about as you go. If this is for other software you might want to reconsider what you install on your computer.
About once a quarter I go to http://winhelp2002.mvps.org/hosts.htm and download a new Hosts file. My internet browsing is so much more peaceful without all the ads.
I use dnsmasq for this. In addition to the speedup from local DNS caching, you can optionally use wildcards to block domains instead of specifying each subdomain.
Here you have a good list, with explanations for some categories.