I had a killer time with all three of my electives.
First was my 'geriatrics' elective... worked with the geri fellows on all their cases. Maybe not a big deal for you, but I really, really love old people... and where I'm going, there sure are a lot of 'em.
Second was my 'education' elective. Running my mouth to medical/PA/nursing students every day. Teaching in the classroom and at bedside. Loved it.
Third was my 'medicolegal' elective. Learned exactly what to say (and more importantly, what not to say) in every sticky situation.
Just my $ 0.02.