There are 10 tools for graphics design,the one which you learn is also there
1.Photoshop
2.Font Doctor
3.Blender 3D
4.BrowserShots
5.BG Patterns
6.Subtle Patterns
7.Adobe Kuler
8.Favicon Generator
9.Basecamp
10.Dropbox
Adobe PhotoShop is the one used most. Many agencies think by default you will have the PSD format when you're done with your work and they will ask for it.
I wanted to add that you need to keep in mind that the mentioned programs are paid. If you wanted to have access to something free, then you may use Gimp.