Skip the pre-configured UIs and use individual mods. Pre-configured UIs usually never have the mods that are a part of them updated/fixed after patches as soon as the mods themselves do. As well as lagging behind mod releases between patches (sometimes far behind).
For an 80 Arcane Mage, I use the following mods:
--For alerting you to when Missile Barrage (and/or Clearcasting) procs as well as the time left on activating it:
GoodNewsEveryone. I used to use
SurgeTrack, but its had some development problems recently.
--For timer bars showing you the stacks and time left on the Arcane Blast debuff:
SpellReminder. If you prefer something different,
Scorchio! 2 is an alternative to this (as mentioned by the above poster).
--For decursing:
Decursive (as mentioned by the above poster).
--For polymorphing (something rarely needed these days unfortunately):
ControlFreak.
--For target/focus target spell bars so you can see when to interrupt/spellsteal, the following. It also replaces your default casting bars:
Quartz.
Quartz also shows you the total cast time of a spell on the bars (for example "
x/2.1"). Which I find invaluable for showing when Heroism cast in your raid/party has expired, you are seeing how different haste equipment affects your cast times, etc..
--For more obvious enemy cast reminders:
FocusInterruptSounds.
--For easy access to your portals without using a ton of action bar buttons:
Broker_Portals (if you don't have a LDB display mod, you can access it through a minimap icon it provides).
That's it. Other mods I use are common across all characters.
--For a personal standard buff/debuff display to replace the Blizzard icons, I use
Simple Buff Bars.
--Threat meter:
Omen (you can very easily adjust the size of its window without a problem. Far more important is setting it to alert you when you cross 90%-110% threat).
--Damage meter:
Recount (you can also very easily adjust the size of its windows). Recount uses a pretty hefty amount of system resources. But it has--for better or worse--become the generally accepted current "standard" for party/raid combat meters.
Using optimal spell rotations (obtained from studying
Elitistjerks), I usually normally hit the "DPS limit" for my equipment as shown by the
Rawr program. The default Blizzard bars I find are more than sufficient for casting/consumable usage/etc.. But if you really want action bars different from/in addition to the Blizzard bars, I recommend
Macaroon!,
Dominos or
Bartender4.