I think what you need depends upon what you want to do. I mainly make historical domestic fireplace cooking things & gardening / farming tools so, for me, the essentials are: Hammers, Forge, Anvil, Chisels, Punches, Vice, Hardy, Tongs, Swage Block, Mandrel, Anvil Tools, Scrolling Tools; in that order.
If you aren't a pro' and want to increase your number of tools and learn new skills at the same time... make them! I have posted a link to the e-book 'Basic Blacksmithing' under the book review section of this website, it is a VERY useful text. I made my first tongs last week, following the instructions in the book, superb!