Yourlensreview - Lens - Peleng 8 F/3.5 Circulair Fisheye

Extremely wide
Reasonable sharp
It works good on small apertures, especially beyond F/8.

Build quality is appalling
It only works good on small apertures.
You have to close the aperture yourself before making a light measurement. This makes framing not impossible, but more difficult.

Sharpness depends on the mount, I've used this lens on 2 of my camera's, an A-mount (KM/Sony) on which it's very unsharp and on an EF-mount (Canon) where it's _alot_ sharper. So even though you can use this lens on many mounts, you have to keep this in mind.

The big vignet is something to keep in mind. On a cropfactor camera the vignet is easily cropped away but you lose some of the extreme wideness.

The picture on this website is my Peleng lens, and you can see the glue sticking out between the front pieces. That tells you enough of the build quality. The only reason why I would give it a 1, is because it feels quite sturdy.

I will still recommend this lens, because it is nice to play with for such little money. Also, it retaines it's (little) value really well. But I'd recommend a better quality fisheye lens if you are willing to pay more. For example the (less extreme) Sigma 15mm is autofocus. And if you own a Nikon, get the 10,5mm.

-Very, very wide, even on crop camera
-Incredible fun effect
-Price

-Tends to be underexposed on borders and overexposed on center
-Front cover falls off way to easy.
-Manual Focus
-Manual diafragma

This little east-european beauty should be in your bag too. Incridible effects.
So wide, you'll probably end up having your feet in the shot if you don't watch out..
Great for making 360 degrees panaroma's, you'll just need 4 shots!
It's wise to shoot in RAW using this baby, to have some room in under/overexposure.

Price
Sharp
Preset Diaphragm

Edge Flare
Manual focus

First, the problem mentioned by Jasper is that the Lens CAP falls off easily.  The Peleng has no lens hood.   The lens takes good pictures for a fraction of the price of the competition but you need to accept things like manual focus.  The Preset Diaphragm is a big step up from Maunual as found on, for example, the Zenitar 16mm but you are still limited to looking trough the dark when shooting.  There is absolutely no reason to buy this lens if you have the cash to pay at least 3X as much for the competition.  I did not have the money and am thrilled with the lens.  On Canon, it meters well in Av or M modes.  I understand this is an issue with some Nikon models (but do not have one to know first hand).   
More: http://home.comcast.net/~dougsmit/fisheye.html

+ Wiiiiiiide
+ Price
+ Fun factor

- Manual focus
- Lens hood

This lens is a great addition to your bag-o-photogear. It is wide, fun and sharp. The distortion you get when you hold this one in front of someone's face (2 cm in front of the nose e.g.) is amazing (no, no samples - friends will not be pleased ;)).
The lenshood is a bit of a worry though. I have to use ducttape to hold the lens and hood together.

Scout eBay for the lowest price and google around a bit if you use a Nikon dSLR (problems with the mirror).

By the way; the samples below are all defished using PTLens (20D with a Zenitar 16mm profile) to get rid of the black corners.