I am not aware of any directory of brandable names.
Some vendors specialize in brandable name transactions. The most known is brandbucket.com with arount 40k 'brandable' names listed. There are a dozen of similar market places, brandroot.com for example.
To some extend, any company name (however terrible) can be considered as brandable, especially if the company is successful. In other words, success provides a certificate of brandability
One step further and you can consider that any pronounceable name is also brandable (or will be if it is successful).
There is some work published on NP to try to predict the value of a brandable domain (based on the letters contained, the length, similarities with previous transactions and other factors). Some predictions are very nice, but the general consensus on NP is that automated valuations are not accurate enough to make business decisions and should be only an indicator among others.
May be you should reformulate your question if you have something specific in mind.