I'm sharing a cabinet with a few other people in one of Hurricane Electric's datacenters. A full cabinet is $400/mo and we split it 7 ways based on space and power consumption.

If you can't get together the people for a full cabinet (which I think is definitely worth it, the more you buy at once, the cheaper it gets), there are a number of providers that offer single server colocation. The only one I've really heard much about though is Joe's Datacenter, which is in Kansas City, Missouri.

Unfortunately there isn't really a "Linode" or "DO" in the colocation space anymore. There used to be https://prgmr.com, which offered transparent pricing based on power and bandwidth usage but they've stopped that I believe. The few global providers are generally geared towards multinational corporations or at least businesses more than small groups or hobbyists. You're really best off with the smaller regional providers near wherever you are.

Assuming that your are not in the middle of nowhere, it is typically best to stick with a somewhat local or regional co-lo facility. Discovering who else has space there is typically a good indicator or quality. Find out where your local hospital or university has their boxes. Keep in mind this is your hardware and it will occasionally need a new HD or fan. You do not want to fly across the country for that. Also their are a wide range of security options for co-los, so weigh those options.

There is no de-facto colocation provider. Peer1 is an example of one that has a lot of locations, but it's not by any means dominant.

Every major urban hub has a multitude of providers. Some offer expensive, but reliable service, others cheap but you get what you pay for, and there's a mix in between. Talk to people and ask for tours. Every town is completely different in terms of scene.