I second all the recommendations for the Terry Brooks collections. I particularly am fond of the Heritage series.
While technically a collection of novellas, the "Wool: Omnibus' is really fantastic. Yes everybody and their mother have raved about it but IMO it actually lives up to the hype. My wife and I sped through it in less than a week.
If you're looking for some fast paced entertaining space opera, I recommend the Robotech omnibus collections:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
If you're into the classics the Delphi Collections are definitely the way to go:
http://www.delphiclassics.com/
Of course I should recommend the user formatted public domain books on Mobileread. If you're into sci fi and fantasy, you need the Savage Sword of Conan Collection and the Barsoom Omnibus:
https://www.mobileread.com/forums/showthread.php?t=31960
https://www.mobileread.com/forums/showthread.php?t=12782
These are formatted better than anything you'll find on amazon including the overpriced Howard reprints which are great hard copies but kindle versions leave a lot to be desired:
http://www.amazon.com/Coming-Conan-C...oming+of+conan