I have completed two mad scientist-types: Dr Frankenstein and a Mad Scientist.
Dr Frankenstein is from Heresy (as Dr Frankenmuller - UNDEAD017), and was very easy to paint. He comes with an arm that you have to attach, and I had a bit of trouble keeping it stuck on. I ended up having to put some filler on the shoulder in order to patch it up a bit.
The next mad scientist model is by far my favourite and had a great time painting the chemical concoction in the flasks (and which I think really makes the miniature "pop"). This is a Reaper miniature (Dr. Ervin Friedman, Mad Scientist - 50046) which was a pleasure to paint.
Both miniatures are on resin bases by Fat Spider.