In the early 1980s Douglas Lenat wrote EURISKO, a program Eliezer called "[maybe] the most sophisticated self-improving AI ever built". The program reportedly had some high-profile successes in various domains, like becoming world champion at a certain wargame or designing good integrated circuits.
Despite requests Lenat never released the source code. You can download an introductory paper: "Why AM and EURISKO appear to work" [PDF]. Honestly, reading it leaves a programmer still mystified about the internal workings of the AI: for example, what does the main loop look like? Researchers supposedly answered such questions in a more detailed publication, "EURISKO: A program that learns new heuristics and domain concepts." Artificial Intelligence (21): pp. 61-98. I couldn't find that paper available for download anywhere, and being in Russia I found it quite tricky to get a paper version. Maybe you Americans will have better luck with your local library? And to the best of my knowledge no one ever succeeded in (or even seriously tried) confirming Lenat's EURISKO results.
Today in 2009 this state of affairs looks laughable. A 30-year-old pivotal breakthrough in a large and important field... that never even got reproduced. What if it was a gigantic case of Clever Hans? How do you know? You're supposed to be a scientist, little one.
So my proposal to the LessWrong community: let's reimplement EURISKO!
We have some competent programmers here, don't we? We have open source tools and languages that weren't around in 1980. We can build an open source implementation available for all to play. In my book this counts as solid progress in the AI field.
Hell, I'd do it on my own if I had the goddamn paper.
Update: RichardKennaway has put Lenat's detailed papers up online, see the comments.
The journal's web site is here, from where I've just downloaded a copy of the paper. I don't know if it's freely available (my university has a subscription), but if anyone wants it and can't get it from the web site, send me an email address to send it to. (EDIT: Now online, see my later comment.)
The paper describes itself as the third in a series, of which the first appeared in the same journal, volume 19, pp.189-249 (also downloaded). The second is in a volume called "Machine Learning", which you can find here, but I haven't checked if the whole book is accessible. (EDIT: sorry, wrong reference, see later comment.)
Personally, I'm deeply sceptical of all work that has ever been done on AI (including the rebranding as AGI), which is why I consider Friendly AI to be a real but remote problem. However, I've no interest in raining on everyone else's parade. If you think you can make it work, go for it!
Isn't the second paper in the series the one immediately before the Eurisko paper, "Theory formation by heuristic search: The nature of heuristics II: Background and examples" by Lenat, volume 21, page 31? Can you download that one?