http://search.games-workshop.com/search?locale=gb&keywords=wings
The 1st 2 sets of wings are easily the best for size.
Both balrog and dragon wings are commonly used.
Also, they are plastic, so wont over balance the model and can be converted easily.
For the jump pack style, engines from aircrafts work.
Either
GW, or any other companies (possibly alot cheaper.)
Neither model is mine, it was just a quick google search.