It's worth for $10, compared to Nikon 105mm f/2.8G ED-IF AF-S VR Micro-Nikkor Lens for $1000.. (Heck, it was less than $800 last year.. the price go up as if it's made of gold..)
50mm f/1.8D to it's end (It was $107 when I bought it in 2008, now it's $160.. insane!). You'll need a lens with an aperture ring (not a G) or the lens would be stuck at the lowest aperture and you won't be able to get any light in. Also, a zoom would be a bad idea due to reasons I point below. 50mm f/1.4D or the 85mm f/1.4D would be slightly better, but the 50mm f/1.8D is the most cost effective.
It's really really difficult to capture something that moves with this extension tube on, and you almost always need strobes to light the subjects. The thing is, with this thing attached, the effective focal length is probably something like 150~160mm and effective aperture at F/1.8 at the lens is probably around F/6, I don't know.. do your math.. anyhow, the DOF is razor thin at F/1.8, and at F/8 and up when you start to get a decent DOF (by decent I mean something like below, the above shots were at F/16 and up) You virtually can't see the subject through the view finder without holding a flashlight at the subject..
(I shot all these at ISO 100, 1/200s and SB600 at full power from side and on camera flash at full power)
And it only focus to like couple of inches to the front of the lens, you can't do much other than shooting small insects and flowers..
I focus by moving the camera back and forth than moving the focus ring as that shifts the frame dramatically.
So, you get my point right? It's not an alternative for a $1000 solution at $10.. but, within a pretty limited scope, you can achieve some amazing results with it.
I bought it on ebay, but here's the amazon link.
There are much expensive tubes with auto focus. But, all you get for that extra money is auto focus, proper metering and aperture reported on your exif. But the limitations in DOF and focus distance would still be there.. At that point, you might just as well throw some cash on a cheap macro lens.