The Rohloff Speedhub is probably the nicest internally geared hub on the market and we happen to have one in the shop (special ordered for a customer) and the moment so we figured it was worth posting a pic here.With 14 evenly spaced gears the Speedhub has practically as much range as a conventional multispeed drivetrain. Conventional drivetrains may have more actual gear combinations, but some of the combinations are more or less redundant, and others have far less than optimal chain lines - both of these issues are completely absent from the Speedhub.
The Speedhub can be mounted on virtually any frame with the use of different OEM adapters, though it's pictured here on the Surly Troll which is built specifically to accommodate the hub without adapters - cool. The Troll can also accommodate 'normal' drivetrains.
The Speedhub may weigh more than a conventional hub but when you add up the weight of high end multispeed drive train pieces like shifters, chainrings, cogset, and derailleurs you realize that the weight difference is negligible. The same goes for cost - the Speedhub isn't cheap, but neither is a really good multispeed set up.
It's also worth noting that the Speedhub uses one external cog of your choice, so even though it's internally geared you can adjust the gear range by using a cog with a different number of teeth.
Internally geared hubs are gaining popularity again as 'adventure' biking becomes increasingly common and riders look for bombproof hubs that keep going no matter the conditions.
If you've always wanted to know what it looks like inside an internally geared system, wonder no more!...here's a video that pulls back the curtain, and it's apparently narrated by the same gal who does all in-flight Air Canada safety announcements, only her accent is German instead of French.