I tend not to have any minis around for very long that I dont like the look of. I usually put stuff that I'm not happy with on ebay and use the money to buy new stuff. This means that there is no real 'chain of improvement' in my painting: from early mishaps to where i am now. I sometimes regret this. I wish sometimes that I had kept the first space marines that i painted when i got back into the hobby last July. It would be good to see the improvement.
So, In answer to the collaborative post, my answer would have to be "...are no longer in my possession". Having said that, rummaging through my painting box I did find my Blood Angels captain, which i suppose is technically the worst example of my painting that I currently still have.
I bought the mini as part of the first Black Reach boxset last year (I've probably bought about 3 more since then). I flogged the rest of the minis early this year, but kept this - no idea why. I can't think of a single thing that i like about it. Everything that i did with it, i now know how to do better; from highlighting to painting skin etc etc. Even the base isn't very good. The cloak has greenstuff on it when i was experimenting with making a cloak for a homemade Vulkan for my Salamanders.
Hopefully there is a big gap between him and Typhus, which is the most recent mini that I've painted.