I'm going to start with weapons first, because as I've said a thousand times, a rogue is his/her weapons. You'll notice that Blizzard has tended to keep items of the same type dropping from the same boss/dungeon, this will make it easy to decide which 5-man you want to run to round out your gear.
In the dagger department, we can find a pair of slow daggers and a pair of fast daggers on the new 5-man dungeon loot lists. Heartshiver (normal Forge of Souls) and Blood Weeper (heroic Forge of Souls) are the slow daggers, which make great MH options. For your OH, which absolutely needs to be as fast as possible due to the new Deadly Poison mechanics, you can pick up Krick's Beetle Stabber (normal Pit of Saron) or the Unsharpened Ice Razor (heroic 5 man trash).
My 5-man group found an Unsharpened Ice Razor on our first playthrough, as well as several other trash epics. It looks like the drop rates of trash epics in these dungeons is fairly high. We also found the fist weapon named Seven-Fingered Claws, which is a viable MH option for a Combat rogue using Close Quarters Combat for their weapon specialization. There weren't any great maces, so it looks like Blizzard has decided to phase them out of the 5-man loot table.
There are two new swords added in ICC's 5 mans, the slow-so-MH Ghoulslicer (normal Halls of Reflection) and the speedy Liar's Tongue (heroic Halls of Reflection). While Liar's Tongue is fairly potent and ilvl 232, the Ghoulslicer is a lowly level 219. Lucky for us, Blizzard also added two axes for rogue usage. In normal Halls of Reflection, you can find a Hate-Forge Cleaver, but it's still only an item level 219. To find a great companion weapon to Liar's Tongue, see if you can score a Nighttime, a slow axe that will suit your Hack and Slash spec perfectly. The Godfather of Souls keeps this axe in the heroic version Forge of Souls.
The Godfather also holds onto the only thrown weapon I could find, but a great one: Papa's Brand New Knife. With Mutilate rogues loving Haste and Attack Power in light of the recent changes, this is perfectly itemized for them. Now if you want to steal a bow like the Crypt Fiend Slayer or the crossbow named Felglacier Bolter, go right ahead, but expect resistance from the hunters in your group.
Once you start raiding Icecrown Citadel, you'll gain access to the Ashen Verdict's reputation rings. These work similar to Karazhan's rings, so you will get an upgraded version at higher reputations. The starter band at 'Friendly', the Ashen Band of Vengeance, is very potent with its hit rating (hard to find in ICC) and high item level. Make sure to watch your reputation and pick this one up quickly. There are also two rings from the new dungeons, the Band of Stained Souls (heroic Pit of Saron) and the Ring of Carnelian and Bone (normal Pit of Saron). While we're at it, Garfrost in the heroic Pit of Saron also holds a great necklace, the Barbed Ymirheim Choker. It's not as good as the Onyxia quest reward, the Sparking Onyxia Tooth Pendant, but not bad nonetheless.
The real draw of the new loot tables are the pair of amazing trinkets available. The Needle-Encrusted Scorpion, which drops from heroic Forge of Souls, is basically a slightly upgraded version of the ubiquitous Mjolnir Runestone. With its Armor Penetration proc, it will allow for any rogue capable of running a simple heroic dungeon with the ability to soft cap their ArPen. Unfortunately, this trinket comes at a time where Combat is 2nd place on the rogue charts, and Mutilate rogues can safely ignore ArPen from their stat list.
The other available trinket, the Herkuml War Token, doesn't even make you rely on luck! This one can be purchased with 60 Emblems of Frost, and is incredibly potent. The 153 Haste is great as is, but 340 Attack Power after a short build-up period makes this trinket a no brainer. I expect many rogues to make this their first Emblem purchase, especially if they weren't lucky enough to score a Death's Choice from ToC25, as ToC didn't really have any other amazing melee trinkets.
Between heroic gear, normal mode items, and the awesome Emblem of Frost leather, there's nearly a piece for every slot. Take chest pieces for example: between Blackened Geist Ribs (normal HoR), Choking Hauberk (heroic HoR), and the 95-Emblem Shadow Seeker's Tunic, you can truly move from 'okay gear' to 'top-shelf epics' while only doing new content. Note that the Emblem items in ICC are fairly expensive, this is offset by the fact that there are many more bosses in ToC than there are in Icecrown, and with the 4-week gating periods between bosses, you'll have plenty of time to farm Emblems of Frost.
If you need new gloves, you can get a pair from normal HoR via the Carpal Tunnelers (a great pun!), though the Cat Burglar's Grips (via 60 Emblems) are quite superior. If you need a new belt, for another 60 Emblems, the Vengeful Noose is waiting for you. An amazing cloak can be scored via 50 Emblems, the Recovered Scarlet Onslaught Cape. Due to a lack of really great capes outside of hard mode content in the last couple of patches, I see this as another great choice for an early Emblem purchase. If you're trying to conserve, there's also the Accursed Crawling Cape from normal Forge of Souls to tide you over.
If you're looking for a pair of shoulders, you can find Bewildering Shoulders (normal FoS) and Spaulders of Black Betrayal (heroic HoR) in the 5 man dungeons. There's also some great Shaggy Wyrmleather Leggings from normal PoS and Fleshwerk Leggings from the heroic version of PoS. Also consider using your old Emblems of Triumph to score a piece of T9 if you're having bad luck with either of these drops.
There's only helmet, the Frayed Scoundrel's Cap from heroic FoS (from the same boss that drops the ArP trinket) that is perfectly itemized for a Mutilate rogue. For boots, you can find Blighted Leather Footpads in the heroic Halls of Reflection after escaping Arthas, though there was also a great pair that dropped from Icehowl in ToC10. Finally, you can also score a decent pair of bracers from the heroic Pit of Saron, and Chewed Leather Wristguards have hit on them too. Hit has become a scarce stat in ICC, and so be sure to evaluate where your hit chance is when considering items and upgrades.
Tier 10: Shadowblade Battlegear:
Our new set, Shadowblade Battlegear, is again purchasable through Emblems alone. The cost has gone up greatly from the Argent Tournament, but so have the set bonuses. The 2 piece bonus is effectively 30 energy a minute, in addition to making it easier to throw out Tricks of the Trade to the raid for a damage boost. With the 2 piece bonus, and the new ruptureless Mutilate builds' viability, the Tricks of the Trade glyph may even become a standard. The 4 piece bonus isn't too shabby either, though it remains to be seen exactly how valuable it can be. With an even mix of stats across each piece of the set, we see that there's only one item with hit rating: Shadowblade Pauldrons. I would recommend moving to 2 pieces of Tier 10 as soon as it is feasible for you, though be sure to compare your gear in a spreadsheet before making that leap. This new gear costs so many emblems that you really don't want to be wasting them on a piece you'll replace quickly.
With so much new gear, it can be overwhelming to know where to start. I would suggest finding your weakest pieces (by stats or by ilvl) and focus on where you can replace those pieces first, and then see what drops as you start to run the 5 mans. There will be a lot of interest in these dungeons over the next few weeks, and with Tricks of the Trade and Kick to offer, rogues will be very popular DPS classes to invite. Be warned, these dungeons are a serious step up in difficulty from what you're used to, and they make ToC look easy.