If you enjoyed A Brief History of Time
, you might enjoy The Elegant Universe
by Brian Greene (I've no idea if it's available as an ebook, and it's Sunday arvo, so if you want to go looking, be my guest
). It becomes "technical" of sorts, as it progresses, but its beauty is that it leads logically and gently into it, such that it doesn't feel like you're drowning in conceptual mindwarps (which is a nifty trick, considering the subject matter
). I actually found it a more enjoyable and a bit easier (though much longer) read than A Brief History of Time
(and that's without denigrating the latter at all).