Rogue Leveling Gear:
You maybe asking what gear to go for when leveling. Generally you will want to concentrate on gear that is high on Agility, Attack Power or Crit. Secondary to that it is always nice to have some extra stamina to allow you to allow you to stay in the fight longer while grinding.
+ Agility = Attack Power, Crit and Dodge bonuses
+ Crit = Increase Chance for getting a critical hit, critical hits do more damage..
+ Attack Power = More damage per hit
+ Haste = Effects fast you attack (haste gear is rare till you get to level 70)
+ to Hit = Mainly effects how much your off hand weapon hits, this is one the most important stats.
+ Stamina = Effects how much HP you have.
+ Strength = Attack power bonus only.(~half as good to have strength as opposed to agility) Leather items with strength are typically made for druids.
+ Dodge = Increases change to dodge, usual leather items with this are made for druid tanks. + dodge is usefully in some situations but do not concentrate on this as it is a wasted state for most things you will do.
To see the effects of each piece of gear check it on the player stat area to see how much equipping a piece changes your stats. There are also some nice mods that shows you the stats in comparison to what you are wearing.
The main reason you do not go dagger in the early levels as a rogue as it is harder to get positioning on mobs. You can only backstab a mob when you are behind it and when you are fighting a mob one on one it will always be facing you except maybe for your initial attack or if you stun it and reposition. You cannot get good sustained DPS by waiting for cheap shot before you can back stab and daggers do far less damage than other weapons for sinister strike/hemo due to their high speed.
At higher levels after you get mutilate if you go assasination, then you can use daggers with a mutilate build and not have to worry about positioning.
End Game Gear:
There are typically 2 sets of gear you may want to have as a rogue, a PVE set for grinding and doing Instances and a PVP set for doing arenas and battle grounds.
The best PVE gear in the game comes from the hardest instances in the game so do not expect to be fully geared fast when you hit level 85. It takes a long time to gear your rogue so have fun with it. Use resources like wowhead or shadow panther to find where your next upgrade and work at getting your gear level up. Typically you can get PVE gear from quests, instances, heroic instances, 10-25 man raids and from reputation rewards.
PVP gear can be acquired by doing battle grounds and arenas. The honor and arena points you get over time can be spent on gear and weapons for PVP. Some of the PVP gear requires arena rankings to be able to buy, so don't think you will just be given the best gear because you PVP it can take a lot of work to earn it.
Shadow Panther is the best page I have found for a site that keeps a current list of the best gear in the game and the rating system he uses is pretty good. He separates his site into many categories for gear for PVP, PVE, what enchants are good, gear sets, consumables, weapons. He also ranks gear using some nice formulas I list below. I suggest going over his site to find upgrades to your gear, looking the gear up on wowhead.com and seeing what is needed to get that gear.
The following formulas and information are from ShadowPanther.net:
AEP vs. DAEP vs. MAEP
AEP (PVP): 1 Stamina = 1 Agility
DAEP (Leveling/5-man): 1 Stamina = 1/2 Agility
MAEP (Maximum DPS Raiding): 1 Stamina = 1/100 Agility
Each stat is given a different weight when compared to Agility. In PVP (AEP), Stamina and Resilience are very important, so they are weighted equal to Agility. In raiding situations (MAEP), Stamina and Resilience aren't worth nearly as much as DPS stats, so they're weighted at just a fraction of Agility.
When looking for gear upgrades, determine what your goal is, then use the chart that works best for you. If your goal is to maximize your PVP gear, then pick items that will give you the largest AEP upgrade. If your goal is to maximize your raid DPS, then select items that will give you the most MAEP. DAEP is somewhere in between, like a compromise for people who want both DPS and survivability.
Listed below are the current versions of these formulas:
AEP Formula: 1 AEP = 1 Agi = 1 Sta = 2 Str = 1.3333 Hit = 1.1111 Crit = 2 AP = 1.1765 Haste = 1.1765 Expertise = 6.6667 Arm Pen = 1 Resil = 666.67 Def = 1000 Dod/Par/Arm/Resist = .0833 B Gem = .10 R/Y Gem = .025 Meta
DAEP Formula: 1 DAEP = 1 Agi = 2 Sta = 2 Str = .8696 Hit = 1.1111 Crit = 2 AP = 1 Haste = 0.8 Expertise = 6.6667 Arm Pen = 666.67 Def = 1000 Resil/Dod/Par/Arm/Resist = .1429 B Gem = .1111 R/Y Gem = .025 Meta
MAEP Formula: 1 MAEP = .9091 Agi = 100 Sta = 1.8182 Str = .8696 Hit = 1.1111 Crit = 2 AP = 1 Haste = 0.8 Expertise = 6.6667 Arm Pen = 666.67 Def = 1000 Resil/Dod/Par/Arm/Resist = .25 B Gem = .1111 R/Y Gem = .025 Meta
Main Hand AEP Formula: 1 AEP = 1 Agi = 100 Sta = 2 Str = .8696 Hit = 1.1111 Crit = 2 AP = 1 Haste = 0.8 Expertise = 6.6667 Arm Pen = 666.67 Def = 1000 Resil/Dod/Par/Arm = .25 B Gem = .1111 R/Y Gem
Dagger AEP Formula: 1 AEP = 1 Agi = 100 Sta = 2 Str = .8696 Hit = 1.1111 Crit = 2 AP = 1 Haste = 0.8 Expertise = 6.6667 Arm Pen = 666.67 Def = 1000 Resil/Dod/Par/Arm = .25 B Gem = .1111 R/Y Gem
Offhand AEP Formula: 1 AEP = 1 Agi = 100 Sta = 2 Str = .8696 Hit = 1.1111 Crit = 2 AP = 1 Haste = 0.8 Expertise = 6.6667 Arm Pen = 666.67 Def = 1000 Resil/Dod/Par/Arm = .25 B Gem = .1111 R/Y Gem