Problem solving contests. The "Regular Expression of The Week" challenge, or solving a Raymond Smullyan logic problem, or smallest program that does X challeng

Problem solving contests. The "Regular Expression of The Week" challenge, or solving a Raymond Smullyan logic problem, or smallest program that does X challenge. You'll have to mix it up to encourage a lot of participation, as some people are scared of regexps, others of number theory, and others of prgramming challenges.