An ongoing challenge for English Language Learners is developing an understanding of, and an ability to use, academic language.
Averil Coxhead from New Zealand has created an excellent Academic Word List site. Just as there are lists and sublists of High Frequency, or Sight, Words (the most commonly used English words) he presents lists and sublists of the most frequently-used academic words.
The lists are good, though there are many other sources of similar lists. The difference here is that he also tons of interactive exercises where Intermediate English Language Learners can practice them.