FlagRSP - An impressive RP addon that allows some interesting RP/IC information to be added to your character's mouse-over info (for others using flagRSP). You can add a last name, a title (e.g. your guild rank), even a short visual description. It will also allow you to change the "level" displays to more "qualitative" descriptions. Furthermore, it can be used to broadcast your "RP level" to others using the addon, from a complete beginner through thoroughly immersed. I strongly suggest that everyone download and install this addon! It's great!
Lore - Lore gives you the ability to speak in 'languages' other than those enabled by Blizzard. It translates your text in /say, /party, /yell and /whisper to a specified user-defined language. If you come up with a good "guild language" for this, let me know and we can add it to the dialects file. It now also adds a "/lang" command to your interface for changing languages.
CT_RaidAssist - Allows you to track health, mana, buffs, and debuffs for all members of a raid group. (All members have to have the addon installed to see all of this info, and at least one member in each group needs it to be able to broadcast health and mana.) This will become more and more useful to us as time goes by.
PvP Cooldown 2 - This simple addon will add a little timer frame when you get pvp flagged, and countdown the amount of time left until you will no longer be flagged. Attacking opposing faction members will reset the timer. After your pvp flag expires, the timer frame disappears until you are flagged again.
Call to Arms - Another great idea for an addon to help people find groups. It's like having a meeting stone everywhere you go, but better! The catch: It relies on other people having the addon installed as well, so... you figure out the rest...
Unfortunate news regarding PlayerQuest and Ephemeral: Both of these addons seem to have fallen behind the most recent WoW patches. They are still usable, to a certain degree, but can be quite difficult at times now. Occasionally, they even result in crashing a player out of the game. I continue to monitor the websites for them, and I know that there are some people trying to fix these problems. I will let you know when they are in more stable versions.
PlayerQuest - allows players to give quests to each other... Wow! (Yes, it's still alpha and a little buggy, not all of the features are implemented and they occasionally break a little, but wow this is an amazing addon! I still can't believe someone is working so hard on this for free. There is a thread in the discussion forum that will help guide you through installing and using this.) Unfortunately, the development of PQ has fallen far behind the WoW updates and seems, to me and a few others, to be too buggy to use. There will be updates on the guild webpage once the developer is able to bring PQ up to a more usable form.
Ephemeral - enhance RP by trading player-created items and books among Ephemeral users. (You need to download the "beta" version, not Ephemeral-PvP. Also, don't use the "whitelist" or "blacklist" since they seem to mess up the communication protocols. If you cannot receive items from someone because a player added you to their whitelist during the transfer of an item, then you will have to relog to resolve this issue.)
Language Command - Language Command adds a command "/lang" to your interface which can be used to switch languages from the command line or in a macro. This version is modified to support Lore languages as well. (Recently, the functionality of "language command" was added in to Lore. If you install Lore, not only do you not need "Language Command," but you should uninstall it.)