Rayquaza and Dragonite.
Depends on what you're trying to do. If you're trying to do very small-group clears, Jynx is probably necessary. Articuno is the best all-around Ice type currently, but Mamoswine (which is incoming) will beat all of these other contenders in all likelihood. I think it's ill-advised to power up any Ice Pokemon at this time.
On the other hand, Rayquaza handles himself pretty well (despite being glassy) and Dragonite is almost as good. Dragon types have more general utility than Ice types and aren't going to be immediately outclassed anytime soon; even if they are, both will still be good options.
EDIT: If you insist on powering up something Ice-type-wise, Piloswine is probably your best bet. It's a serviceable Ice type in its own right and does well against Rayquaza with access to Avalanche, and the dust won't be wasted because you can just evolve to Mamoswine when it comes out.