Where to install additional photoshop fonts: Once you have become familiar with editing in photoshop, you might want to start adding new font styles. Just yesterday, a friend of mine who is relatively new to photoshop had asked "How do I add additional fonts to photoshop". Knowing that there are probably many other people out there wanting to know the answer, I figured I would post a quick response here on the site.
Typically people add fonts to the Windows fonts directory. Fonts placed here can be used for many applications including photoshop. However, if you have a lot of fonts installed, this can sacrifice Windows performance. The good news is that photoshop does have it's own font folder for fonts that you plan to use with photoshop only.
Adobe Photoshop font folder:
Place the fonts you want to use with photoshop in the following folder:
C:\Program Files\Common Files\Adobe\Fonts
Restart photoshop and enjoy the new fonts!
Note: If the "C:\Program Files\Common Files\Adobe\Fonts" folder doesn't exist, simply create it. Adobe Photoshop CS5 and newer versions do not contain this Font folder by default (instead you will see FontsRecommended and FontsRequired folders), in which case, you still need to create the Fonts folder.