Of course, Thailand has more bootleg DVDs than most other countries combined but, I'm not talking about bootleg DVDs, but instead the authentic, genuine article. Pick up a few Thai movies on DVD (just chck to make sure they have English subtitles first), as they're as cheap as 100 baht ($3.10) or, if you're a fan of CSI, Gray's Anatomy, Gilmore Girls, Private Practice, Lie to Me or any number of other American TV series, you can pick up a whole season for as cheap as 299 baht ($10.30). And yes, these are the authentic, genuine deal -- just made for the Thai market, so cheaper.
Also don't miss checking out DVD stalls that pop up in the mezzanine areas of Bangkok's markets. Again, if the DVDs are encased in plastic wrapping, they are genuine and, nowadays, are going for as little as 39 baht ($1.30) for older movies. I just bought The Rock, The Departed, Babel, Resident Evil, and The Bourne Conspiracy - all for only $1.30 each.
DVDs will have both English and Thai soundtrack, as well as subtitles in both languages.