I thought this might be helpful for new people going into raids, or people who are raiding now and are wondering what addons they should have without getting too fancy with imba UI and such
Here is the first addon which most people have now a days which can be the most useful and save your life in many cases, its a simple threat meter that works quite effectively but you should only use it as a guideline, which i have found out after using it for a long time.
http://www-en.curse-gaming.com/downloads/details/4204/
You can modify how small it is on your UI and it will tell you how much % of agro you have before u take agro off the main tank.
The next i find is very useful in end game raiding is Deadly Boss Mods, this can do many things from telling you how close you are to someone such as at a gruul fight so you do not have to judge how far you should move away to telling you how long until a boss may cast something, such as blast nova at magtheridon, this addon is priceless and is useful in many occasions and i would reccomend it to anyone.
http://www-en.curse-gaming.com/downloads/details/4940/
and also i still use CT-mod because i like its simplicity and what it can do, i mainly use it because if it shows the percentage of health of your target, and your target of target, it shows their mana if possible and it also shows you your own health and mana / rage / energy on the bars without you having to hover your mouse over them.This can be downloaded here
http://www.ctmod.net/downloads/
I hope these all become helpful for your raids.
Also another addon which isnt going to help you so much in raids, but its a decent damage meter, that can also record pet damage so hunters can see what damage they are really doing.
http://wow-en.curse-gaming.com/downloads/details/2091/
it can be modified in how it looks quite alot.
Have fun.
Not sure if i posted this in the right place