I'm playing a Level 4 Half-Elf Harrier Battlemind. I'm pretty happy with him all up, tanky, hard to hit, doesn't do a huge amount of damage, but can fairly reliably hit his targets.
My biggest stumbling block, is that my opportunity attacks feel pretty much useless, because my melee basic attack only has a +8 to hit bonus and the damage is 1d8+4, whereas my at-will Battlemind abilities have a +11 to hit bonus and are generally 1d8+6 damage. I've had a bit of a look but can't find anything that would allow me to use one of my Battlemind abilities for the opportunity attack. They are all at-will standard actions. I have Shade Strike, Iron Fist, and World Slipping Advance.
To be clear, this would only be useful when enemies are moving past me to try and attack my allies, if they are committing an attack on my allies, it'd be more efficient and damaging to use Mind Spike, because I have Bolstering Spike, so I get temporary hit points when I use it.