I will have to respectfully disagree with Rasyr, though, and advise you to go through the various companions, all of which I think can be used simultaneously to enhance an RM2 campaign.
I know some people--perhaps many people--see a power creep in the companions, but honestly, I don't quite see it myself. What I do see is that many of the classes in the companions are better at combat than some of the classes in the core rules. That is true. But I always thought some of the classes in the core rules were rather underpowered (yes, Ranger, I'm looking in your direction!), so the power of the classes in the companions seems to me to be generally good and corrective. And in terms of power creep, I don't see the classes in the later companions as being stronger than those in the earlier companions. Rolemaster Companion I has the Paladin, the Archmage and the High Warrior Monk; Companion II has the Warrior Mage. These are arguably the most powerful (or overpowered, depending on your perspective) classes in the game. Later companions have some good ones as well (I'd agree with Rasyr here that the Forcemage is a very powerful class, though I wouldn't personally say overpowered), but in general it seems to me to be more accurate to say that some classes in the companions in general are very powerful. I don't really see a steady power creep myself.
But that's just my 2 cents.
I make this post just because I wanted the OP to know that some of us play with pretty much all the companion classes and don't really have any great problems in doing so. It all depends on how you run your game... so give the companions a look. IMHO, all the companions have something to offer, and you can use them all, if you're careful.
Cheers