You know, looking at Jynx and then looking at Electivire and Magmortar, I'm a little scared to know what a Jynx evolution would actually look like. I mean, barring stealing ideas from Digimon, what we'd probably get is a massive beast that vaguely looks like its middle stage, only with more fur put in random places.
Either that or a caricature of a stereotypical old woman... which is just as alarming.
I guess what I'm trying to say is that while I look at Electabuzz and Magmar and can see evolutions for them, it's a little more difficult to figure out how a Jynx evolution would actually be designed. Personally, I think she's complete as it is -- as in, you really can't take her design much further.
Unless, of course, you decide to go with the Metal Coat, Scizor-esque evolution someone mentioned earlier and have an armor-plated valkyrie Pokemon. Which would actually be infinitely cool.