I made one of the DIY ring flashes out of a dome lamp with great results. Unfortunately, it's bulky and doesn't carry well in the field. I keep it in my vehicle and either use it for on-the-spot shots or when I hold onto something to take to a spot for better photos.
In the image below, you see the main body at the right, a reflective "insert" to adapt it to a macro twin-lite style flash in the middle, and my 430ex II with off-shoe cord on the left.
Rainbow snake with ring flash
Hatchling terrapin with ring flash
Copperheads with ring flash
Brimley's chorus frog with macro twin-lite insert.
Oustalet's chameleon with MTL insert
Scarlet king with MTL insert
When getting much closer with macro lenses, especially with the more reflective individuals, I prefer the MTL insert. It deadens much of the flash's power, but still works and gives off a nice, soft light. It also lacks the ring-shaped flash reflection that can be a little bit distracting with the ring flash.
Now I'm interested in these beauty lamps.