I'd stick with the generic WotLK herbs, specifically Adder's Tongue, Goldclover and Tiger Lily.

In general they're more common then Icethorn or Lichbloom, which means cheaper most of the time. From an Inscription point of view, all five will mill into the same thing.

The Alchemist is more likely to go with cheaper recipes to level. I did not make BC era Flasks (using the more rare BC herbs), while leveling my alchemy. I'm guessing Frost Lotus will be rather rare, once Northrend is as dead as Outland is now, so many of the Icethorn/Lichbloom recipes won't be a viable means to leveling.



The Northrend items should all skyrocket in price, but will take a while to reach their peak value.
When the majority of new toons in Cataclysm (Worgen/Goblins, but also Tauren Paladins, Human Hunters and the like) reach the 375-450 trade skill range, that will be the time to sell.
I'm planning on selling Northrend items between Week 5 and Week 8 of the expansion.