As Dev Null raids continue to progress, it's important that people make SMART choices about gear. Less playing time does not negate the need to make smart gear choices. Assuming that Tier 4, 5, or 6 is best is sadly incorrect in many cases. It's also important that people understand how gear for their class works so that you can roll with confidence that the item is truly an upgrade for you. Just because an item comes from a higher level dungeon does NOT make it automatically better than gear from lower levels. If you are unsure if an item is an upgrade, pass on the item and research it before it drops again.

Dev Null is filled with people who understand gear selection for their own and sometimes other classes -- they would be happy to share that with you. It's important for everyone to understand that for every class there is more than one correct "mindset" for proper gearing, and opinions will vary from person to person. Work together with other toons of your class/spec to share and adopt new theories on gearing. Its' also VITALLY important that people disconnect their toon from themselves so that suggestions can be taken without offense.  Be open to trying new ideas.

If you toon is under performing, please take the time to visit the appropriate sites listed below and talk with other people about improvement. It is Dev Null's goal to spread quality loot with everyone who wishes to take part in the raids, but that comes with the responsibility of making smart loot choices. Our guild is moving forward in progression, and we have a very long time to continue that progress before the expansion hits. We want EVERYBODY to be a part of that progression, but Blizzard has designed many fights to REQUIRE a certain level of performance from EVERY toon present to beat. Carrying poorly performing or inattentive toons makes difficult content even more challenging, so let us help streamline your play style and gear so we can put forth a solid group effort!

To that end, please take some time to look at some of the following websites. I myself have found many of these to be very useful in making gear choices for my own toons, as well as pointing out shortcomings or oversights I have made in gemming, enchanting, talents, and casting sequence.

http://be.imba.hu This site loads your toons data from the Wow Armory, points out weaknesses in gems, enchants, and hit rating. Sometimes offers suggestions on talents, and gives a fairly generic overview of where that toon should be raiding. It's not without flaws, tending to prefer dps oriented gems and enchants over survivability (stamina), and it's PVE placement overview is purely based on the iLVL of your items. Higher iLVL is not a guarantee that the item is better.

http://www.maxdps.com This one is only available for certain classes/specs. You input your stats, weapon dps, weapon speed, hit, haste, spell damage, expertise, crit, etc, and select notable talents you have, and it calculates your theoretical max dps, miss rate, dodge, resists, etc. It also shows how much dps you would gain from +10 of any stat. It's important to realize that it's highly unlikely that anyone will actually hit their theoretical max dps in game, mostly due to waiting for tank aggro, fears and other cc, run time between mobs, lag, which keeps you from dpsing continually. The site also can suggest upgrades for your current gear, but again it's based purely on iLVL which is an unreliable method of determining upgrades.

http://www.lootrank.com/wow/rank.asp This site, suggested by Molpe, appears to be a great way to find upgrades for your gear and is ranked by calculated score, not iLVL. Once you have your settings made, you can save them for future use, or use a premade class template.

For Tanking Warriors:
http://www.devnullguild.com/modules.php?name=Forums&file=viewtopic&t=868 This is a Tanking Warrior gear chart made by our own Talisfears/Taliafears. You can use this to find meaningful upgrades and isn't sorted by iLVL, but rather actual calculations based on combat log observations. Any questions to validity could be directed to Talia himself, and he'd be more than happy to explain how he determined the results.

http://www.tankspot.com/forums/gear-lists-rankings/32083-berg-s-tank-gear-rankings-03-19-2008-wow-2-4-a.html Another take at a tanking gear list.
http://elitistjerks.com/f31/t18771-protection_warrior/ Great tanking information with solid mathematical calculations.

For DPS Warriors:
http://www.devnullguild.com/modules.php?name=Forums&file=viewtopic&t=868 This is similar to the tanking chart above, but for dps warriors and is still in development, also by Talia.

For Rogues:
http://www.devnullguild.com/modules.php?name=Forums&file=viewtopic&t=422 Another great chart by Talia, I believe it's values are based on a Combat spec.
http://www.shadowpanther.net/   All information sneaky and rogue-like, including gear and weapon charts.  Should be useful for all specs, not just combat.

For Enhancement Shaman:
http://www.devnullguild.com/modules.php?name=Forums&file=viewtopic&t=1349 Similar to the charts above, but made by Vespra (with a bit of legwork from me). It's important to note that this particular chart ignores stats that don't contribute directly to dps, like stamina, intellect, and mana regen.

For Warlocks (with more of an emphasis on destruction builds):
http://wowmb.net/forums/showthread.php?t=23586 This has nice calculated gear lists, and gear suggestions at each tier of raiding, as well as a sample gear selection for each raid level. It's important that you understand how spell hit works, and where the cap is when it no longer benefits you. The lists are generated assuming you are not hit-capped, so once you reach that cap the rankings may not be as accurate in providing dps upgrades.

For Druids:
http://druid.wikispaces.com Lots of useful info here for all specs.
http://www.emmerald.net/Bear_Mitigation/Head.html Bear tanking gear charts.
http://www.emmerald.net/Cat_DPS/Head.html Kitty DPS charts.
http://druid.wikispaces.com/Healing+Gear+List Healing Druid lists.

For Shadow Priests:
http://www.shadowpriest.com/ Shadow Priest forums
http://www.shadowpriest.com/viewtopic.php?t=9844 Raid gear list from those forums.

For healers in general:
http://healcrafter.com/index.html Another one I am unfamiliar with, suggested by Molpe. It appears to help calculate mana/5, how much regen to expect over the fight's duration, and how much raw healing you should be able to provide with your current stats.

I am not aware of any gear charts or lists specifically for Mages, Hunters, or Paladins. If you know a good site with meaningful information, post on the forums and we can get it listed here.