I improved my reading speed a great deal after reading a book by Tony Buzan (probably called Speed Reading). That book also discusses mind mapping to improve comprehension and later on remembering what you learned from the text.
I also wrote an article a long time ago about doubling your reading speed. It can be found on my blog:
Double Your Reading Speed Now
Subvocalization was already covered, but focus is just as important. You won't be able to go through a certain text quickly if you're constantly drifting off. Another tip is not to worry about comprehension the first time you read a text. Better to read a certain text at a higher speed than once very slowly.