There are 15 different rarities that Pokemon has used within the past 4 years.  The top 6 rarities (energies, C/UC, RH C/UC, R, RH R, and HR) are the rarities that are most commonly sold for bulk, C/UC being the most frequent.  


Basic Energy
Reverse energies go under RH C/UC
No Symbol
180 g / 6.5 oz per 100 cards


Common / Uncommon (C/UC)
Includes: Trainers & Special Energy
 / Uncommon
180 g / 6.5 oz per 100 cards


Reverse Holo Common /
Uncommon (RH C/UC)
 / Uncommon
190 g / 6.7 oz per 100 cards


Rare (R)
Rare
180 g / 6.5 oz per 100 cards

Reverse Holo Rare (RH R)
Rare
190 g / 6.5 oz per 100 cards
Holo Rare (HR)
Rare
190 g / 6.5 oz per 100 cards

Promo


Prism
Rare


EX
Rare


Full Art EX (FA EX)
Rare


Mega EX (M)
Rare


Full Art Mega EX (FA M)
Rare


GX
Rare


Full Art GX (FA GX)
Rare


Hyper Rare GX 
(HR GX, RR , or RR GX)
Rare


Special Notes:
    • Some companies might take promos as holos, but confirm with the company before you package up your cards. 
    • Most stores do not accept World Championship or foreign language cards, but you may ask the person you are working with if they do. 

Additional Information: 
Card Mavin - Has detailed pictures about rarity symbols, and where they are located.  
Virginia Pokemon - shows pictures of the different rarities, and key distinguishing features. 
Flipsidegaming.com - Has a longer explanation for each era of cards, so if you have older cards, check this out.