TotalRP2 - Creats a custom flag, letting you pick a last name, Title, Prefix, description and Roleplying status. This can also show your background story, states (If you are sad, trustworthy and so on) these states are placed on your name plate as small icons. Lets you set your own personality chart, make quests, NPC talks and speeches, create items too - Doesn't work with MyRoleplay or Flags (Only displays it's own) And will make your name look more interesting to others using it.

Example:
Without TRP2 - [Guild] [Gehco]: Hey Guys!
With TRP2 - [Guild] [Gehco Quel'Dron]: Hey Guys!

And remember to keep it up to date or it will make conflicts with Tongues. (Basicly it's Verisimilar, MRP, GHI all-in-one)
http://wow.curse.com/downloads/wow-addons/details/totalrp2.aspx

MyRoleplay - Creats a custom flag, letting you pick a last name, Title, Prefix, description and Roleplying status. Also allows you to write in age detail, race (if diffrent than what you are) birthplace and where you are dwelling now - Doesn't work with FlagRSP, or X-perl, TotalRP.
http://wow.curse.com/downloads/wow-addons/details/my-role-play.aspx

Tongues - An AddOn that allows you to speak diffrent languages, and lets you learn diffrent languages as you listen to people talk in the own tongue. Has an easy UI, a big red button.

A few examples:
- Wolf
- Cat
- Kalimag
- Serpent

And -MANY- more, even use Horde/Alliance languages on within you faction, though avoid it.

Does make a conflict if your TRP2 isn't up to date. Sometimes mixes up the languages.
http://wow.curse.com/downloads/wow-addons/details/tongues.aspx

Gryphonheart Items - An AddOn that allows you to create your very own items to trade between people using the same AddOn. (If you carry a Flag through MRP, TRP, FlagRSP, do write is you have GHI, might give people a chance for recieving some fun items)
Doesn't work together with other item making tools, but this seem to be the most popular.
Gryphonheart Items may confict with WoW-UI, it can bug and make you unable to trade items that ain't GHI items.
http://wow.curse.com/downloads/wow-addons/details/ghi.aspx

Verisimilar - used for creating custom quests and NPC speeches and talks.
It may create conflicts with TRP2 as they implemented the same feature. Just be sure it's up to date and nothing should happen.
http://wow.curse.com/downloads/wow-addons/details/verisimilar.aspx

FlagRSP Cataclysm - Creats a custom flag, letting you pick a last name, Title, Prefix, description and Roleplying status. Same as totalRP and MyRoleplay (Work with TRP2, not MRP) Have never experience conflicts with this one, though it might appear annoying at moments if you have it on pop-up as you move your mouse over people who have it.
http://wow.curse.com/downloads/wow-addons/details/flagrsp.aspx

SpeakingSpell - Allows you to make customizable yells, says, and emotes that trigger on a % when doing in-game actions. An example would be to make Tardon have a 50% to say "Die heathen!" and a 50% chance to say "By fire be purged!" whenever I get a killing blow. These can be added to almost any in-game actions.
http://wow.curse.com/downloads/wow-addons/details/speakinspell.aspx

LanguageCycle - easy way to switch between languages, just by one click. By default it also uses Common/Orcish in /party, /raid and /guild chats, even if you'd be speaking the language of your race in /say - I have been testing this, it doesn't seem to conflict with anything as of yet.
http://wow.curse.com/downloads/wow-addons/details/languagecycle.aspx

Aubcom's Environment Emotes - a very simple, low-maintenance addon that reformats emotes on your side for a subtle yet awesome immersion effect. (Plays well with Prat! I was told) I do not know about any conflicts yet.

Example:
It changes emotes in the format of:
/e || The birds won’t fly tonight.
Into:
The birds won’t fly tonight. (John)
Instead of:
John || The birds won’t fly tonight.

In addition, emotes such as:
/e 's nose is far too big for her face.
Will now appear as:
Jane’s nose is far too big for her face.
Instead of the usual:
Jane 's nose is far too big for her face.

http://wow.curse.com/downloads/wow-addons/details/environment-emotes.aspx