Depends on what the niche is. For my own sites, heavy on the Facebook, plus I maintain contacts with all the local news media via Twitter, Facebook and email. Some of my enterprises have t-shirts and other items, all of which have my URLs on it.
For clients - again, depends on the niche. My biggest has published an 84-100 page catalog once a month for like 30 years - they didn't stop once they went online, they just went from sending 15k a month to 125k a month. Plus they have cultivated around 100K opt in email addresses for a weekly email blast.
I have B2B clients doing well with LinkedIn, and everyone does well with PPC if I'm the one managing it.
My brother works as a chef for a local restaurant, and he and I are planning to set up an Instagram account for the place so he can shoot pics out from the kitchen. Another eatery I know tweets out "code words" and if you get there within half an hour with the code word, you get a free something or a discount.
Still other clients have put their products into Amazon, figuring if you can't fight the beast, might as well join.
I've partnered up with other sites and other companies to co-market stuff. Been asked to guest blog, but I just don't have time for it. But done right, it can be a good tool. If you're local, there are usually all kinds of places you can hook up with to either share costs or trade services or reciprocate marketing.