There are a ton of options out there for rendering. I have tried quite a few and these are the options that I have come to use the most. Keep in mind that these are generally geared towards smaller projects that you may do with a small team or solo.
When I do my solo projects for customers, I enjoy the benefit of a render farm. It is quick, easy and reliable. I don’t have to house the hardware and I can pay as I go.
I am only going to recommend one commercial render farm. The one that I use is Renderstreet or render.st. The reason why I like them is thanks to their model. You pay a monthly fee, then you can render as much as you want within that period. At the time of this writing their offer is $50 per month. There is a limit though. For still images a render cannot take more than 1 hour, and animation frames cannot take longer than 15 minutes. Fair enough for most projects, and there are also offers to increase the time limits if this is a constraint for you.
They also have priority rendering where you can pay per hour for prioritized rendering without time limits. The prices are reasonable and the option is good to have if a deadline is closing in. The combination of these two options make a solid render farm offer.
If instead you want some more control, I would suggest trying out barista. Barista is a Blender add-on that sets up a mini cloud for you on the Amazon EC2 cloud. Barista creates the virtual machines needed and have them render your project. Then it shuts off the virtual machines to keep the cost low. The add-on goes for $89.99 and after that, all you pay is for the EC2 server time with Amazons fees on their service. Barista cuts away the middle man and goes straight for the computing power.
The downside here is that you don’t have a render farm that can support you. You only have the add-on support, and they don’t have full control. A more risky alternative, but a cool idea that is also pretty cheap.
The third alternative is Sheepit render farm. Sheep.it is a free render farm that works with a points' system. You download a small piece of software that recognizes your hardware and allows your computer to be part of the render farm. Then you rent out your hardware in exchange for points. The amount of points you have then determines how high your projects get prioritized.
Most of the time, a couple of frames rendered is enough to bring you reasonably up the queue on Sheepit.
The benefit of free is quite clear but there are some issues here, so only use this for hobby or personal projects. For a commercial project you might have security concerns. After all, your projects get uploaded to other peoples computers.
How long your render will take to complete may vary quite a bit as well. You might be unlucky and have a bunch of high priority accounts rendering long animations when you want to squeeze out a couple of frames. Some things to keep in mind, but for personal and happy with no security concerns, give it a shot.