Yet another for Calibre.
I also suggest trying out BookDesigner for creation of ebooks from substandard sources. The output is LRF, but using Calibre, one can make ePub from the LRF file. It's still how I create all of my own eBooks (from legitimate and perfectly legal and morally sound source materials, thank you very much). The learning curve is fairly steep, but with a little practice, and HarryT's BD Tutorial (which can be found here on MR:
https://www.mobileread.com/forums/showthread.php?t=11678&highlight=Book+Designer+tut orial) one can really make some fantastic books.