DBM and Omen are the 2 you need hands-down. Everything else is for convenience or cosmetic use. You could argue that those 2 are for convenience too, but they are too helpful to not require.
Well im raiding with my dk and soon my warrior and i dont want too use a compilation that others have done and i want to know what addons is the most important ones too have on the screen like recount dbs etc.....??
Yeah, I'd pretty much second that as essentials.
Other than that, I use Mik's Scrolling Battle text and ClassTimers for cooldown monitoring.
RNGesus - Saving you unreliably since BC.
Agreed - DBM and Omen for sure.
I use xPerl raid frames, and place my target frame, and target's target frames near my toon's feet. Omen lives directly below that. Between them, I can tell at a glance who has how much threat on my target, and therefore know when I need to concentrate on one, whether it's safe to tab over to a secondary target, and if that secondary target is being tanked (and by whom), or if I need to/gather it up.
Simple setup. And surprisingly efficient at telling you what you need to know at a glance.
Omen and DBM are a must. I also believe that MIK SCT is a must. With Runestrike macroed to all attacks we don't see it proc and I for one just like to know that its happening . I'm still a big fan of OmniCC as well. Xperl is one of the best raid tools out there in my opinion. It's raid bars, cast bars, target bars, alert and monitors allow me to see what healing is going on to the raid and myself as well as see all dps targeting and dmging the boss. Ever been privy to the "I stopped dpsing!" argument that dpsers have. This can be solved right and quick. If your looking for something to clean it up a bit, I would not recommend skinner. It has been throwing errors on me like you would not believe. I subbed out to nothing in the hopes something like the old aperture would come out again.
Not that another /agree is needed, but yah, if nothing else, DBM and Omen.