It is about 10 years that I am using WordPress for web-design. Here is a list of websites which I use frequently:
1- Google
I do not know how can I solve my technical problems without Google ! You can find the answer of almost any technical question with it.
2- Newsletters
I have added my email to the subscription list of these website. It helps me to keep myself up-to-date and fresh.
3. I optimize the images of website with imagecompressor.com everyday. It’s great, fast and free.
4- Unaplash.com is a great source for professional free photos.
5- Browsing ThemeForest and CodeCanyon helps me to know more about new products, plugins and themes.
6- Google search console to analyze the traffic situation of clients’ websites.
7- GTMetrix to analyze the performance of websites.
8- Ahrefs and Ubersuggest free tools.