As I imported the names of all the known exoplanets into freebase, the pattern was very apparent. In most cases, Exoplanets are named after their parent star, such as 51 Pegasi b (51 Peg b for short), where the parent star is 51 Pegasi, and the last letter "denotes" the planet in chronological order of discovery. You would never find a capital "A" planet because it denotes the parent star itself. Thus, the first planet that is detected upon a star is named as "[star_name] b". The succeeding exoplanets to be discovered in that solar system will then follow the alphabetical sequence for it's designated letter. Example: Gliese 876 b and Gliese 876 c was discovered in 2000, Gliese 876 d in 2005.
Some exoplanets were named after the telescope used in detecting them, such as TrES-1 (detected by via microlensing), or SWEEPS-11 and WASP-3 b (using the Transit Method).
To poetically end this post, An exoplanet by any other name would smell as extra-sweet!