Nice to see some sketchbook style threads around here... I think they're a great thing for any forum.

Nice pieces so far.

Have you ever considered trying to sculpt something from scratch? Without a predefined base mesh? It's great for unplanned creative outbursts... not that I'm saying it's a better way of modeling, having a solid base mesh is very important for the production environment... but it's still good fun if you're just doodling.