A GitHub blog, usefull to me, hope the same for you.
What is special with Shadertoy is the community, animated by IQ and other big contributors. They are present on the site to comment the newly published shaders, and it’s really cool. The facebook and Twitter community is also very active. There is a Discord server. The technical limitations introduced by the GLSL language also avoid to have a too large creations. For example building a complete game is very painfull and a true challenge. For this, the published shaders are mainly simple, few line of code, centered on procedurals technics, performance tricks aesthetic and colors. The ergonomy of the site is also great, with Alt+ENTER shortcut to compile in a second and see the results, making possible to spend hours making a step by step improvements to your art work until to reach the perfection !
When you publish a shader, all is made to make it visible and attractive on the site.
I like the community of Shadertoy, so even if more featured sites may exist, there is no better place for me today than Shadertoy to post a shader !
Below alternative sites I noticed