Best tool / software for making ebook?

I'm planning on packaging several blog posts into an ebook. I'll definitely have a PDF version but am open to other formats as well, I just don't know much about making ebooks.

Is there any good software for converting html into ebooks? Or should I just copy / paste into a word processor and then convert to PDF?

Is there an easy way to package spreadsheets into the ebook? Maybe something more user-friendly than zipping files or having multiple separate files?