For some reason I’ve always wanted to play with object-oriented persistence into relational tables. This is when you code in an OO style and your objects are automatically persisted into a RDBMS tables without you having to write SQL – the framework converts your object structure back and forth. I wrote a simple class set for h2g2 but I’ve never used any proper frameworks for it. Tangram is a popular system for Perl which Jo recommended; I haven’t really had an excuse to use it yet. There are various systems for Java, since OR is well-suited to J2EE Entity beans, and Hibernate looks really good: very feature-rich, and the documentation definitely talks the talk.