I am not a beginner to chess, but I have found myself stuck in a rut playing the same opening over and over.  I begin with 1..e4 and turn it into a 3 or 4 knights game.  I have found this opening to be well rounded and it sets a good pace for my games, but  I would like to try new stuff.  Can anyone point me in the direction of a well balanced opening that is slow and steady?

Najdorf!

Next steps might be the Scotch Gambit (d4) and Giocco Piano (Bc4). After that the Ruy Lopez with Bb5 which is perhaps the richest openning system in chess. It's a must know for an e4 player.

What ever you decide to rally, it should lead to an imbalance of some sort (superior minor piece or pawn sac for development/initiative e.g.)  that you could nurture leading you to a stronger position than your opponent.

You need to try d4 though and the queen's gambit. I used to play e4 everytime until I learned the nuances of d4 and that suited my style more. Overall there's much less theory to learn than e4. The main setup is d4, c4, e3, Bd3, Nf3, Nc3, 0-0, maybe Bg5 or Bb2 via b3, and an eventual e4. Play goes on from here and It's usually quite comfortable and slightly better for white.