Normally, the best gear drops in the hardest instances, or from final bosses. However, every now and then you get a real surprise that drops from an easier opponent.
As everyone should know by now, Flame Leviathan is the first boss in Ulduar. Despite the higher difficulty of Ulduar, Flame Leviathan by itself is not too bad, and kind of fun. If at all possible, you should try and get into a 10-man run of him every week. He drops a surprisingly good trinket for rogues – the Pyrite Infuser.
Its another AP proc, much like Mirror of Truth, but with a higher number (1234 AP for 10 seconds). In addition the trinket gives an enormous amount of hit raitng (95) on equip. Hit rating is never a bad thing. In particular, if you have been gemming for +hit to get you to the poison cap, then this item will allow you to re-gem for other stats.
The various loot ranking systems (Loot Rank, Shadowpanther, Gear Wish List) rank this trinket higher than all of the pre-Ulduar trinkets except DMC:G and Bandit’s Insignia, and right around or slightly higher than Grim Toll and FFF. That’s not bad for a drop from the first boss in a 10-man raid.
I don’t know if Flame Leviathan is reliably puggable yet. It may take a month or so before enough people know the fight to make it something I’d pug. But even if your guild isn’t ready for the whole of Ulduar yet, try to get them to go in just for 10-man Flame Leviathan and see if you can’t get this great item.