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To start with using addons is not considered cheating unless they violate any rules and regulations of WoW. They mearly add ease to exploring the wonderfull world of Warcraft. Some of the addons that might be necesay are Atlas/Atlas Loot, Cartographer, Auctioneer(one of the most valuble addons if not the most valuble!), Bagnon, QuestHelper and if you are into raids and instances Omen  threat meter. The last one is a Class helper. Being a rogue I use Rogue focus, but there are many other ones for all classes. Atlas and AtlasLoot are ingame addons that display the loot tables for the dungeons and raids. Using this would indefinitly help knowing what items drop from which boss/mini-boss. Cartographer is another valuble addon that is an enhanced version of the ingame map displaying coordinates across the map. Most websites that display data on quest use coodinates to show the locations of key quest items. This brings us to quest helper, although it wont tell you what quest you should take it tells you the general area of the quest ie. kill 10 wither bark trolls. For those it shows the general area, but for quest needing specific items like tablets and scribings it shows the exact place and uses  an arrow(placed where you choose n the screen) to guide  you to your destination. For Auctioneer, well what can i say? It is almost a neccesity to making gold in WoW. Auctioneer saves prices while you look at items in the Auction House. Example While your looking at prices of Mithril Ore it saves the prices it sees and gives you a rough estimate of what price you should sell your stack for. I t has many features that would be invaluble to yuor success in WoW. Just check it out.   

Oh great, I have been wanting a threat meter that works well. Whenever I have my lock, I have to be very careful to not do too much damage cuz I can easily pull aggro onto myself and get instant killed by just about anything. There are consequences to my reckless all damage, no armor spec. I love auctioneer cuz I'm an auction tycoon. Cartographer is also a really useful map addon. Atlas gives you a huge edge by being able to see maps of the dungeons. And I haven't tried Quest Helper yet but that looks so useful. Thanks for all the info. This is really good stuff.

Something to keep in mind about threat meters is that it requires that party mates also have the threat meter - they operate upon reading the abilities performed as stated in the combat log and assimilating the information for visual display to show players where they are in relation to other members of their party/raid group.

 Omen is one of the most popular because it is also backwards compatible with the most commonly used threat meter used pre-BC (KTM Threat Meter). Omen also is updated regularly, be sure to check wowace frequently for a new version!

I find that as a healer, I am always recommending a unit frame mod. I used AG_unitframes for my party and switched to Grid (another wowace mod) when in a raid. Grid is one of the most powerful raid frames without taking away your ability to play the game. It tracks important things such as hot's, incoming heals, and aggro gained. I found the aggro warning upon raid members invaluable when healing a raid.

Other common mods include proximo for arenas, deadly boss mods for raiding, hawksy recap for a damage meter, simplechat for a chatmod and there are a slew of bar mods if it is your desire to move or change the display of your buttons. Personally, I use trinity.

Thanks for the info. Healing mods make a healer's life SO much easier when you can see who's taking what damage. I'm glad to get some of the tools of the trade from a pro.

I used to have a really fun addon that would put up custom symbols on characters or enemies when they had certain buffs/debuffs on them. It was really useful because I could visually see which HOTs I needed to throw up on which character. I could also track my DOTs on enemies from my lock. I just wish I could remember the name of the addon...