Melee in Naxx:
First off - YOU ARE DOING IT WRONG!! (Just for you Dale!!)
Next - do your homework. that means going to a website (I recommend wowwiki),learn the fights,read the strategies, understand what is involved,because:
Your most important stat is not Attack Power,Crit or even Hit Rating - it's Situational awareness.
A lot of fights in Naxx require even more attentiveness than normal, the tank is going to have to move mobs constantly and you need to stay up with them, or you will get a debuff that requires you to run out of the raid...and then there's The Safety Dance
You need to be constantly on your toes and know exactly what is going on - not only to yourself but also the raid in general. If you can't focus on what's going on around you, you will die. And dead folks do no DPS
Next comes hit rating - I can't emphasize how important this stat is. All the crit rating and Attack Power means NOTHING if you cannot hit the boss. For melee you want between 8 and 9 percent. This is not a negotiable stat - you NEED a minimum of 8 percent for bosses in Naxxramas. Most melee gear of blue quality and heroics will get you there, also there are enchants and gems as well. On of the best weapons for Retribution Paladins, Arms Warriors and Titan Grip Fury Warriors is a Titansteel Destroyer. Good DPS, Decent stats and most importantly a nice +54 Hit Rating. For rogues and enhancement shamans you may consider the titansteel maces or the Saronite Shiv or Savage Cobalt Slicer. Slap Accuracy enchants on the 1handers and you are set.
Attack Power and Crit are interchangeable importance wise depending on your class. I think a minimum of 2000 AP and 25 percent crit is an acceptable milestone. It's incredibly easy to achieve that especially considering the vast amount of food,flasks and other consumables availible...which brings us to:
Consumables and enchants! There are various and sundry leg enchants available - as melee dps you want the ones giving you AP and crit. Period. For flasks look for Endless Rage, or Relentless Assault if funds are low. For head enchants - the Arcanum of Torment (Knights Of The Ebon Blade Revered) and for the shoulders the Lesser Inscription Of The Ax (Sons Of Hodir honored). Also consider Blacksmithing as a tadeskill, not only for the ability to manufacture some good dps gear but also for the ability to add gem slots to your gear. If not a smith, at least purchase the belt buckle that is smith created. More gem slots is a good thing!!
Some people preach love and respect. Me? I just hit you with my giant hammer.