Let me first tell you what almost everyone will tell you. Play what you enjoy. Truly and sincerely, the more you like the class, the more fun you're going to have. There's room for everyone in the raid scene, and every class is needed.
That being said, cleric is the number one most needed class in the game. Period. There are never enough clerics. After that it's kind of situational, but you you could almost always use another warrior or bard. Once you start getting some items, I've heard warrior can actually be quite busy. It's not just hitting taunt and kick like a lot of warriors did back in the old days.
http://wiki.project1999.com/Sakuragi%27s_Warrior_Guide is a pretty great guide if you're interested in the class.
But really, I can't reiterate just how important it is that you pick a class that you're going to have fun playing. In this game more than any other I've played, that's the most important piece of advice I could give you. Hope to see you in Norrath =).