Here are some links of downloadable e-books in English and ELT.
1. Introduction to Linguistics (Edward Stabler, 2010)
2. An Introduction to Syntactic Analysis and Theory (Koopman, Sportiche, and Stabler, 2003)
3. The Official Dictionary of Unofficial English (Barrett, 2006)
4. How Language Works (Gasser, 2006)
5. Spell Well (Fields, 2005)
6. Write Like a Pro (Riley, 2013)
7. Improve Your Writing Skill (Nikitina, 2012)
8. Psycholinguistics 101 (Cowles, 2010)
9. Metaphor (Ritchie, 2013)
10. Intercultural Communication (Samovar, Porter and McDaniel, 2011)
11. Discourse and Social Change (Fairclough, 1993)
12. Academic Vocabulary (Olsen, 2009)
13. Interactive Vocabulary (Olsen, 2009)
14. Correction, A Positive Approach to Language Mistake (Bartram, 1991)
15. Reading Their Way (Dorothy J. Donat, 2003)
16. Spelling in Use (Lester Luminack and Katie Wood, 1996)
17. Whole Language, Whole Person (Maya Pancheva and Todor Shopov, 2003)
18. Newspaper Journalism, A Practical Introduction (Susan Pape and Sue Featherstone, 2005)