What mobi readers for PC are there?

Free eBook Reader: http://www.fbreader.org/

Calibre: http://calibre-ebook.com/

And then, of course, you could just use the Kindle software: http://www.amazon.com/gp/feature.html/ref=kcp_pc_mkt_lnd?docId=1000426311

I have tried PDB, Mobi, EPUB, Djvu with Sumatra PDF. Its simple, starts fast.

Official description:

Sumatra PDF is a free PDF, eBook (ePub, Mobi), XPS, DjVu, CHM, Comic Book (CBZ and CBR) reader for Windows. Sumatra PDF is powerful, small, portable and starts up very fast. Simplicity of the user interface has a high priority.