As u/ChefM53 said, the spices you want will depend on what types of food you want to make.
I like making spice rubs for meats and Indian, Middle Eastern, and African curries. 660 Curries gave me a great list of spices that I want to keep around to be able to make most curries.
What I keep stocked (and really, one purchase every 2 years is plenty). You can get most of the spices in the first list cheap from an Indian grocery. These show up across cuisines, so are good investments for the flexibility you get:
Also, I keep some spices relevant to Chinese and Korean cooking:
660 Curries is awesome for learning about the ingredients, especially the spices, in Indian curries. Iyer goes into lots of detail about how spices will give different flavors depending on how they're used.
660 Curries is my go-to for Indian curries. Iyer does a great job of discussing the different spice blends and how to prepare them, and identifies the region of each dish.
VahChef is fun an approachable for cooking videos. He's a bit famous for his drunk chicken vid, which is hilarious, but he does great sober cooking too.
For Indian (which you didn't specify, but is essential for mastering spices), Raghavan Iyer's 660 Curries is spectacular because he gives detailed information on what each spice is like, how to prepare it in different ways, and how to make fundamental spice blends (masalas) for Indian cooking.
660 Curries is an awesome way to not only learn how to cook some types of Indian food, but to understand how to prepare and use many types of spices and spice blends.
660 Curries is a great way to learn about the various spices and ingredients used in Indian cuisine, as well as common spice blends (masalas) that are used. Iyer breaks them down in a really great conversational way that makes complex recipes much more approachable.