I like running a close range Keeper -- it's not the most effective, but I like the hectic fun of being up close. I'd Barrier the group, then go into the fray with the tanks and cast Disruption Field. Move back a bit out of the bubble and use Fade Cloak and you can stand still for quite a while before being forced to move. This lets you use Winter Stillness and Gathering of Storms for really fast cooldowns.
So it's Barrier, Disruption Bubble, and Fade Cloak, all upgraded, with the last skill up to taste.
For my usage it's a toss up between Chain Lightning and Frozen Step. Chain Lightning is the most versatile, as it's useful on both ranged and melee attackers and provides decent damage and minor shock control. Frozen Step is especially nice for getting in and putting down Disruption Field on the dangerous archers, and for repositioning when both Fade Cloak and DF are on cooldown. Static Cage is so nice, but does too little against Ranged attackers. Veil Strike does too little for its long cool down to do much.
Lately, I've been guilty of playing around with Mind Blast as the fourth skill. I say guilty, because it leaves this build too weak against ranged attackers. However, it's pretty fun against melee guys that unfairly bee-line toward the Keeper. Especially nice is using it to combo after Mana Surge freezes a group trying to mob you. Too bad Mind Blast doesn't have any effect on projectiles; it'd actually make this a very viable defensive build.