There's always Calibre[1], but it's really bloated. It's a very powerful and capable ebook management system though, it's just not really Mac-ish.

Adobe has a very good ePub reader, called 'Adobe Digital Editions'[2] that runs on Mac, Windows and (I assume) Linux. It's an Adobe Flash/Air application and is much prettier than Calibre. If you don't mind Flash on your mac (I gave up last year), It's currently the best choice.

[1]: http://calibre-ebook.com/

[2]: http://www.adobe.com/products/digitaleditions/

[edit] No, there's no Linux version. You can use it with WINE though; use the instructions here: http://ubuntuforums.org/showthread.php?t=701191

Thanks. Isn't ePub just zipped xml/html? Why aren't there more choices? Seems like a wrapped Webkit would do the trick. Or maybe people just don't read much on PCs anymore.

It's more than just a zipped xml+css+html. There's a total mess underneath that open format specification (toc, item-references, etc).

Use Calibre (right click -> tweak ePub -> explode ePub), or eCub[1] to see and manipulate what's inside an epub...

[1]: http://www.juliansmart.com/ecub#mac

Adobe Digital Editions runs just great and is always handy. I don't get how no one else is doing something like it.

I've not used it, but http://itunes.apple.com/au/app/kitabu/id492498910?mt=12 looks nice, and it's free.

If you just want to read, Amazon's free Kindle.app is by far the best Mac reader. Use KindleGen[1] to convert .epub to .mobi (or scroll up, someone's already done this here).

However, be warned that it won't allow you to copy text even from an non-DRMed ebook, which is quite silly and makes it useless for anything that has code samples in it. For reading a book on screen it's pretty good though.

[1] http://www.amazon.com/gp/feature.html?ie=UTF8&docId=1000...

Readmill is really well designed, though it isn't yet updated for the new iPad.