I've used a total of four CHM viewers up to now. Although I've seen people who read it by first converting it into plain HTML or even PDF, I have one very important reason why I prefer to see a vanilla CHM. Indexes and searches. The CHM format, albeit Microsoft's child, is really a great format for reading docs. It has everything you need to quickly search through a doc file and find what you need.

Chmsee, my CHM viewer of choice: Chmesee is one of the more pleasant CHM viewers under Linux.

Of the CHM viewers I've used, most of them behave more-or less the same, because they all use chmlib to render the CHM files. However, the interfaces differ slightly.

Xchm has long been the viewer of my choice, because I don't use a fully featured desktop environment, so I needed something light on DE-specific dependencies. It gets the job done, but it's not the prettiest of them all.

Chmsee is also great. (And, yes, their homepage is in Chinese. And no, I cannot read Chinese, I just guessed it was its homepage.) It's not as light as Xchm, but definitely lighter than other desktop-specific ones. It's also based on GTK+ rather than GTK 1.0, so it looks better than Xchm.

Finally there are GnoCHM for Gnome desktop and KchmViewer for KDE. Both I used extensively in the past and they are a good choice if you already have installed Gnome or KDE.

I'm not aware of any other tool for viewing CHM files under (Arch) Linux, but those should be enough for any user. CHMs don't offer anything that is not covered with any of the four tools above. Perosnally, I currently use Chmsee, because it looks better, but there's also nothing wrong with Xchm. If you're looking for light, consider using Xchm.