The Electronic Frontier Foundation (EFF) has released a tool, dubbed 'Switzerland' (net neutrality - geddit?), that's designed to help web users check if their ISPs are doing nasty things with traffic filtering, a la Comcast.

The tool (get it here) is open-source, cross-platform and billed as "general purpose ISP testing".

From the press release:

"The sad truth is that the FCC is ill-equipped to detect ISPs interfering with your Internet connection," said Fred von Lohmann, EFF Senior Intellectual Property Attorney. "It's up to concerned Internet users to investigate possible network neutrality violations, and EFF's Switzerland software is designed to help with that effort. Comcast isn't the first, and certainly won't be the last, ISP to meddle surreptitiously with its subscribers' Internet communications for its own benefit."

I've downloaded it but it does look awfully fiddly - I'll let you know what I think once I've devoted some proper time to it.