| Outside of Irontooth, most of the published encounters seem reasonable in difficulty. If you're routinely getting the better of your PCs while following the standard rules, chances are you're using significantly better tactics. The first thing I would do is identify precisely where your particular PCs are going wrong. I have found that one common problem is that new players are not aware of all their options. They forget about Second Wind. They forget about action points. They think the charge action still requires both their move action and their standard action. They don't know that they can make a DC 10 Heal check to activate an unconscious ally's Second Wind. I would start by ensuring your players aren't simply missing an available option, before you start trying to teach them better tactics.
Another option is to start using weaker tactics for the monsters. Particularly with groups that role-play their PCs' combat decisions instead of powergaming them, I also use "in character" tactics for their enemies. For example, zombies mindlessly attack the nearest PC unless otherwise directed. Even most humanoids routinely underestimate the PCs, seeing the fighter as an enemy level 1 soldier instead of a level 1 Fighter, therefore failing to focus fire effectively. Only for highly trained military organizations would I unleash the full brunt of my tactical acumen on my unsuspecting PCs!
I wish I could tell you that just by following the rules that everyone would have fun. For a while I DMed as though this were true. Unfortunately, one reason DMing is hard is that no rule system can guarantee fun, at least not nearly so well as a DM that can read the players' body language and adapt on the fly.
Good luck! | 
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