Although DnD5e.info will hopefully provide the solution to your SRD needs, there are a number of other websites that can also help. Below are some D&D links that I use myself.
Have you even created home brew rules or campaigns? Of course you have, we all have. Not all of us are good at layout and graphic design though. That’s where the Homebrewery comes in. This brilliantly put together website, from Scott Tolksdorf, helps you create an almost official-looking supplement. Perhaps best of all? It’s free! (Although you can support the creator’s Patreon.)
An online combat tracker for 5th Edition. Great if you have a laptop or tablet on the DM side of the screen and even better if you have another device on the other side of the screen. I’ve used my Surface Pro 4 on the DM side and an old 7″ tablet on the other. Again, this resource is free but you can support the creator’s Patreon.
If you’re running your game from your laptop/tablet then the Kobold Fight Club was the perfect addition to your DM arsenal. Unfortunately, the original is no longer with us, but a new version has appeared to take its place. Even if you prefer not to have a laptop at the table, then you can still use it during prep as it calculates the XP costs for encounters taking some of the strain out the heavy lifting. They have a Ko-Fi page where you can support them.
Looking for a random NPC to fill out the tavern or marketplace? Maybe you need some inspiration for a scenario or two. DM Heroes can provide just this. Each refresh of the page brings with it a randomly generated NPC complete with portrait, features, traits and even adventure hooks. Again, another great free resource that you can support through Patreon.
If you plan on running one of the official campaigns released by Wizards of the Coast then I can highly recommend Justin Alexander’s website. He has written “Remixes” of a number of the campaigns that can be of great assistance to DMs. He also has other articles that are always worth reading. You can support him through his Patreon.