Anyway, here is what I currently use in arena after much tweaking.

Jamba: Obvious reasons, not rly useful to have running in arena, but meh too lazy to turn off.
Pitbull: Has the best party cast bars by far... which I use more than I realize to see if my guys are aligned or not, rather than actually looking at my guys. (notcasting = not aligned = bad)
Macaroon: Love it, need it, cant live without it. Best written mod I've ever used. Anyone not using macaroon is a fool son.
eCastingbar: Old school, dependable, highly customizable casting bars for player/target/focus/mirror (breath/fatigue etc). Have always loved this mod.
Gladius: Obviously for lack of a better option. Mainstream arena mod. Everything about it is great... except not always showing rez casting (FAIL), and does not have the ability to update player health once they die(if you make a few kills... and the enemy gets a couple rezs off.... GL trying to keep track of whats going on lol)
Kollektiv Spellalert: Flashes a spell icon + enemy name for any blacklisted enemy spellcasts in the area. Was slightly outdated but I believe it has been updated recently. (works perfect everywhere but arena it seems, in WG I get messages from hordies 100yards away... its sweet)
CDT(cooldowntimers): Shows small customizable countdown bars for spells and items currently on CD, but the GREAT feature for arena, since I never have time to check bars, is you can set this to FLASH a 1sec icon (of abilities coming off cooldown) across the middle of your screen. Main thing Ive found is useful... subconsciously reminding me to re-lay groundings in mid fight.... which in 5v5 is easy to forget once you start zerging.
DBM(deadlybossmods): All around great mod for bgs/arena/whatever. I cant live without my "countdown to arena gates opening" bar. Reminds me to mount up :P
PRAT 3.0: Chat window mods. Cleans up and condenses the chat windows. Timestamps, improved fonts, etc.
POSTAL: Mailbox mod. Opens all mails, etc.
TinyTip: Improved mouseover tooltip. Shows (anchored on mouse) target name, level etc. Nice feature I like is that is shows who the mouseover target is targeting, but without having to click on them. Useful for checking to see if someone is inspecting you.. without lowering yourself to their level by clicking on them :P
SpamMeNot: Hilarious addon for those annoying cross server cry babies. Blocks messages from lvl 1 alts, and responds with a funny "you've been blocked" msg. I have mine set so they would have to level to 5 to whisper me. Still waiting to see if anyone is actually angry enough to do this... lol.
TotemTimers: More useful in small arenas where you normally micromanage totems, but still useful in 5s to indicate if you're getting totemstomped.

I checked out the Tidy Plates explanation and photo... looks like a winner I'll try that this week and let you know what I think for 5v5. Default nameplates are definately a huge issue and hinderance for 5v5 boxing.

To you guys: Let me know if anyone has nice, dependable mods for the following:
- Something to get rid of red error msg spam (ie. "you have no target", "not enough mana" etc... red text, not audio)
- Something to prevent error messages from EVER showing. I use swatter debug mod which changes the error box.. but it still pops up. I want them disabled in arena when I'm button mashing.
- Any sort of dependable rez-casting alert. Something that pops a Raidwarning message would be ideal... but just something that works 100% of the time unlike gladius.
- I'll think of more.