In terms of the recruiters section, whilst I appreciate you may not have had a good experience, this is probably the way a lot of people get contracting work, at least until you have a fairly big network of contacts.
I'd be more interested in knowing what agencies do have a good reputation / good developer experience along with the note to beware of the cowboys.
Funny. I've had lots of problems with Hays. Cancelling cheques, unenforceable and ridiculous clauses in contracts for example.
The best agencies? None. Don't use them if you can help it. If you have to the smaller the boutique ones tend to be better, if nothing else because they'll have the better clients and more interesting projects.
I did a quick review of agencies 2 yrs back to use as we started to run out of organic references in London - Oxford Knight, Burns Sheehan, Recworks (Java and grads) seemed decent. Stack Overflow is also worth using carefully
They're all pretty good as an ex-contractor in the UK. Even getting paid is quite easy if you sub your timesheets quickly.
The killer is simply making sure that if you do the entire 6 month contract in 2 weeks that you still get paid for the rest or have a massive termination fee in the contract.
It depends on your market sector as well. Some agencies are better for banking contracts, others for, say, media.
I also think that it is worth forming a good relationship with a particular agent. Meet in person if you can so they can see you are someone who seems competent. And if you ever have a friend that is looking, it does no harm to refer them to a good agent you know.
I'd be more interested in knowing what agencies do have a good reputation / good developer experience along with the note to beware of the cowboys.