Something that makes it easy to set up my own transforming proxies using a few simple rules. Like yahoo pipes, but more oriented towards manipulating websites rather than feeds.
Could you be a bit more specific on what you mean by "transforming proxies" ?
A proxy that would change parts of the page. Specifically I'm thinking something to make the web more useful from my Kindle, so rewrite new-window links into regular ones, replace links to PDFs with google docs, and maybe simplify pages a bit (article mode is pretty good at that to be fair). I guess "instapaper in proxy form" would also solve the problem.
Probably fairly niche, but it was the first thing I could think of.
Find local (amateur) vegetable growers so we could swap vegetables. I'm overrun with jalepenos, green peppers and tomatoes... would love to trade them for something else.