By my count, there are 40 new fonts (over and above the former “built in” set) for use in Final Cut Pro and Motion 5. They are:
AvenirBlackOblique.ttf
AvianoSansBold.ttf
Bank Gothic Light.ttf
Bank Gothic Medium.ttf
BasicCommercialLTCom-Bold.ttf
BeaufortPro.ttf
BebasNeue.otf
Bradley Hand Bold.ttf
Brush Script.ttf
DDT-bold.ttf
DDT-condensedsemibold.ttf
EngraversGothic-Regular.ttf
ForgottenFuturist.ttc
Franklin Gothic Demibold.ttf
GaramondRoughHEF-Medium.ttf
GaramondRoughHEF-Reg.ttf
GillSansUltraBold.ttf
Handwriting Dakota.ttf
HopperScript.ttf
Junegull.ttc
Loopiejuice-Regular.ttf
Luminari-Regular.ttf
OctinSpraypaint.ttc
OctinStencil.ttc
OldEnglishText-Regular.ttf
OperinaPro.ttf
Phosphate.ttc
Posterboard.ttf
SabonLTPro-Roman.ttf
Shababa.ttf
Shabash Pro Regular.ttf
Sinzano.ttc
SketchBlock-Light.ttf
Snell Roundhand.ttc
Soap.ttc
Trattatello.ttf
VIP.ttf
Virtus-Regular.otf
Wanted.ttc
Zingende Light.ttf
The fonts with .ttc extensions are TrueType collections (multiple weights/styles, usually but not always).
Apple changed the location of the included fonts within FCPX and Motion from their locations in versions 10.0.9/5.0.7 and earlier. To include these fonts with your system fonts, You can find the new collection set in:
Final Cut Pro (or Motion) application; right click to Show Package Contents, then: Contents / Frameworks / Flexo.framework / Versions / A / Resources / Fonts
Use Font Book to install. I recommend creating a new “collection” and naming it FCPX Collection (it is guaranteed that all users of Final Cut and Motion will have access to these specific fonts — if you need to share projects.)
Hope this helps!