Cross-class skills for summoner

[Shizuna]

As people previously have said, Raging Strike and Swiftcast is a must have

The other ones I picked up are:
Blizzard II - Helps when you want to AoE a bit more when there's 3 or more targets, but don't spam it cause you waste a lot of mp doing that a lot.
Surecast - Situational, like for example when you're taking a large amount of damage (ie: From T5 Twintania fireball), use this so your cast will go through. Good for PvP as well if you're getting interrupted.
Quelling Strikes - You don't really need this, since summoners doesn't grab aggro easily. Use it, if you find that tanks (especially low geared tanks) can't multi-aggro cause of your AoE... o_O