I've been PVPing the last few weeks in my grinding spec (3/0/58), and with the start of Season 4 decided to actually do Arena for once. Seeing where my problems have been so far, I decided on a 0/17/44 spec, with the standard frost talents, and Impact and Molten Shields being the key parts out of the fire tree.
I'd considered the standard 17/0/44, or 0/0/61 specs, but they didn't seem to solve my problems, specifically, Warriors swinging Stormherald, Combat Rogues, and SL-SL warlocks.
I've played around in BGs for a few hours, and this spec seems to do everything I want, I keep my survivability, and get stuns off of Molten Shields often enough to be obvious (the ranged stuns especially).
I'm quite please with how my frost talents are working, but would like some advice on the fire talents. Impact and Molten Shields are fairly obvious, as is Improved Fire Blast. I picked up Incinerate and Flame Throwing as extra crit is always nice, and the extended range really helps bring Fire Blast in line with Ice Lance. Ignite was basically a filler, as was Pyroblast (I've used it twice so far, on sheep) I intentionally skipped Burning Soul, as the interrupt resistance only applies to non-instant Fire spells, of which I only (and rarely) cast Pyro.
I've considered going fire down to Blazing Speed, but don't really think it's worth giving up my Water Elemental for it. Arcane is similar, in that the only really useful talent I can get with the talent points available is Improved Counterspell, and it hasn't seemed worth it for just the one spell.
If anyone has a critiques or suggestions, please let me know (and why you think that'll be better). I plan on using this build for Dailies, Arena, and occasional BGs. For my current gear, please see my mage, Hikari. For now, it looks like my partner will probably be a Shadowstep Rogue. At least until I can transfer to my brothers server, then it'll be his Frost Mage, or Protection Pally