Whew...this thread itself was a read! Thanks to everyone for the great recommendations.
Probably not too important anymore, but I noticed Poul Anderson's
Tau Zero was mentioned a while back, with the statement that it wasn't available as an e-book. That was quickly corrected, as Baen has it under a different name, apparently. For the record, it is also now on Amazon under the original name, and for a downright decent price. Some of his other books, I see, are there for a similar price (less than $6).
http://www.amazon.com/Tau-Zero-ebook...9191533&sr=1-1