I guess the most obvious would be the GW defiler & soulgrinder legs, which have all ball socket joints.
Maybe too steampunk for you, but they are really rather good indeed, as they can be made so that they can be reposed... ( so you can make your spider walk, climb or pick things up on the table.... )
Im sure they have been used many times for Wild Wild West style mechanical spiders, but they may be too large for what you are looking for?
Worth seeing in the flesh though, as as a resource for making 28mm mechanical spiders they are rather fab.....