I was in a similar situation a few weeks ago on ebay. What I considered where: battery grip, black rapid camera strap, remote flash trigger, or a better beamer. In the end I went against all suggestions and what I first thought I wanted and got an off camera flash cord. It has already come in handy on a few shoots, since its the first time I have been able to get my flash off camera, and Im happy I chose it, plus it was the cheapest and I was able to buy another item(not photography related though).

The strap is awesome if you carry your gear around a lot and want it ready quickly.
I think the Better Beamer is only a good suggestion if you do wildlife photography.