My IRC bot used reddit's own search api, but restricted to a handful of subreddits like eli5, askscience, and askreddit. I also used a bit of machine learning to improve the results a bit, by predicting whether or not a post would have a good answer. It was based on just a few simple features like the number of n-grams that matched in the title, the body, and the number of votes, etc.

It was on the #lesswrong irc for some time and people loved to play with it, until eventually a fun hating op muted it.

Sample conversation: https://i.imgur.com/LDD9isL.jpg