Well there's a huge coincidence.
Finding myself in a similar position just a couple of weeks ago, I bought three to try.

1) Item 170952978688 was a 7mm borescope from xcsource that cost about £17.
It comes with the "Supereyes" software. It just a cable with the slim camera module on the end - no flexible gooseneck or handle. It really is tiny at only 7mm thickness.
It's really not bad for the price and if you only have an 8mm hole/bore to work with then there is not much else. However it's one big downside is that it has a fixed focus set for an optimal range of a few cm. Depth of field on the image is not too bad but it's not enough to give you a clear view into a large space. In practice this is very limiting unless you have just the right problem.

2) Item 320641865864 Was a £30 "Snake Vision" kit consisting of a camera on the end of a flexible gooseneck mounted on a handle. Comes in a nice moulded plastic box with attachments of mirror, magnet, and hook (I've not used those yet). It is quite a handy gadget, mainly because it is easily steerable and can reach way back into openings, on high ledges, or under things on the floor, behind fitted units etc. Still not focussable but it's depth of field seems much better. I'm quite pleased with this. It is great for looking into inaccessible places but not so useful for looking through holes you drill because the camera is 14mm thick.

3) Is available on ebay although I bough mine from eachbuyer. It is one of these
http://www.supereyes.cc/en/b005-multifunction-usb-portable-digital-microscope-23.html
It comes with a white plastic cone thing and a pretty useless little tripod.
This scope is actually the most useful for me so far for peering through holes drilled in plaster/reveals because it is only 10mm thick and has a manual focus adjustment from < 1cm to infinity. Nice sharp images. The "pen" format makes it very easy to handle though of course you don't have the long reach you get on the SnakeVision scope.

They are all only 640x480 pixel resolution but that has been plenty enough for the job so far. I would recommend item 2 or 3 depending on the nature of the inaccessible places you want to go looking.

All three have adjustable LED lighting built in. These work well enough.
Only the ultra-cheap and tiny 7mm thick one claims to be waterproof although I haven't tried it in wet conditions.

I notice that model is actually a SuperEyes TE15. It uses the same software (and Windows driver) as the pen-scope item 3) that I liked.

All three come with Windows PC software.
Oh, and the SuperEyes scopes do seem to be recognised as a standard USB camera by an Apple Macbook too. I didn't manage to get the SnakeVision working on a Mac.
The SuperEyes models claim to be compatible with Linux too although I haven't tried that.

I use a Sealey automotive hand held unit at work. It has a screen, a 1m flexible shaft and a 6mm camera head. It has a few other little add on bits.

It is OK. No better, no worse. It really depends on what you want to do with it. Fine for exploring tight spaces, but no good for more open spaces (due to focal range). Also, which way is up? Sounds silly, but once you have used one of these, you will know what I mean.

Only as good as the operator generally speaking. We like the one we use as the 6mm head is really useful for getting into really small spaces, or for minimal damage to linings.