Before you get started with your massive plan for 2010, take a few minutes to go over your rogue's bank and inventory. You may have a few odd items around that you saved just in case you 'needed the hit' or if some hybrid Strength build became en vogue. Clear out plenty of inventory and bank space to prepare yourself for the upcoming expansion. While you're at it, evaluate your current tradeskills as well. It's a perfect time to redo your professions to min/max your damage, with Jewelcrafting and Blacksmithing typically taking the lead for effectiveness due to their flexibility. I'm currently a Miner / Engineer, and while Engineering actually has some powerful DPS perks (cheap boot/cloak/glove enchants), Mining is just about useless. If I get some free time, I'll be dropping it for a superior profession immediately.
You don't forget about your other important skills, either. Lockpicking has become a dying art, and so raising it to the cap proves that you're serious about your rogue and you respect the traditions set in place by thousands of rogues before you. Having all of your weapon skills maxed out also allows you to easily swap between any weapons and spec, so ensure you've trained with every weapon available.
If you saw the video I linked a few months back, you saw some amazing aerial kills where a rogue used Killing Spree mixed with some engineering goodies to blow a target out of the sky. Druids, shamans, and mages lost their ability to knock targets off of their flying mounts, and so rogues are truly the last class left capable of assassinating an airborne target. Go spec Combat, equip two super slow weapons, and coat both with Wound or Instant Poison. Find some unsuspecting Alliance or Horde coward fleeing via flying mount, and blow them out of the sky before they even know what's happened. Keep some Noggenfogger Elixir around so you don't slam violently into the ground: reserve that honor for your victim.
You should also take an hour or two and go on an assassination run in an enemy capital city. Mutilate and Subtlety builds are perfect for this, especially as Sub's stealth-enhancing talents will let you move more quickly and with a lower chance of being detected. If you're on a PvE server, you may have to wait until a PvP-flagged target appears in your view. Avoid the thief-catchers, mark your target for death, wait until they walk into an empty hallway or a dark corridor, and release them from the burden of living. There are some great shay coves in Ironforge that work perfectly for this, and the Flight Master tower in Orgrimmar is totally unprotected. Enjoy knowing that no other class can truly perfect the silent kill as a rogue can, and that some scum from the enemy faction is cursing your name as they make the long walk back from Dun Morogh or Durotar.
If you're looking for some additional PvP action to get your shadowy blood racing, find a rogue partner and queue up for some 2v2 arenas as the double-assassin combo. Very few arena team comps strike as much fear into the hearts of their opponents as a pair of invisible killers. Have fun trying to CC one off target while eviscerating another, and enjoy the fact that rogue/rogue is just about the only double-class combo that actually works.
Nostalgia and experimentation:
We're going to see some pretty major changes to Azeroth when Cataclysm is released, so take this opportunity to visit some of the famous sites that have shaped us as rogues forever. If you haven't yet paid tribute to the master assassins at Ravenholdt's secret monastery, make your way through the Hillsbrad Foothills and show your support. Blackrock Mountain is likely to see some of the biggest changes of all, as many of its inhabitants are strong lore characters in the new expansion. Because of this, I'd also suggest going back to Blackrock Depths for one last Plugger kill, and cross your fingers for the Barman Shanker to finally drop.
With Mastery and the brand new talent trees radically redesigning what a rogue build looks like, take this downtime to explore a spec you've never tried before. Equip a dagger and mess around with Shadow Dance / Backstab or try out a flavor of Mutilate PvP you haven't worked with before. Depending on how drastically we see our trees changed, it may be your last chance to truly experience every build the rogue has to offer.
There's plenty to do before we see Cataclysm released, and that's not even including the rest of Icecrown Citadel and Season 8's eminent release. If there's anything you've ever wanted to try or really regret missing, I suggest you make a list as your New Year's Resolution and start checking off tasks as soon as possible. It's a rogue's job to strike fear into the heart of our enemy, and so go forth and make the opposing faction wish they had never logged in.