I am looking for a good and stable threadpool library for C++ that\'s fairly well documented. I know about the Native Windows thread pool API and the newer Vista Thread Poo
Intel TBB is another threading library that has some neat stuff. I find the framework for evaluating a tree of expressions in parallell especially nice.
With respect to the boost thread pool: this link might be useful: http://think-async.com/Asio/Recipes
A portable threadpool library that claims to be 'production ready'. You may want to check that out.
There's also ACE which does thread-pooling over networks, so it's a fair bit more complex. (but deserves mentioning here, IMO)
Qt has a threading library with some nice high-level operations like map/reduce etc, as well as low-level threading stuff and thread-pool support.
Qt might be a bit big for you though, but you can use a part of it pretty easily.
Have a look at the ThreadPool and TaskManager classes from the Poco C++ libraries.