I started writing this article, thinking I would eliminate item pieces from which you couldn't get an equivalent emblem piece. This left me with basically feet items, and weapons. due to a simple overlook, I also realized even feet items and weapons could be bought. Silly me, however I do believe those pieces and trinkets and rings, and even back pieces tends to be some of the hardest to come by. This is due to no small part that the valor and heroism vendors give very lame pieces for their cost, especially that shifty valor vendor.
Instead of telling you what pieces to get, I'm going to guide recommendations. In general every class of every spec is going to want to hit the tier 9 four piece, and then get either a 245 helmet or 245 shoulder. I'll let you use your best judgment. Personally I went with the 245 shoulders, because the tier 10 shoulders are cheap, and gets you half way to that tier 10 2 piece bonus if you so wish. You should also pick up the "ranged" slot piece and a single ring from that triumph vendor.
Get that trinket too, unless you're a healer. If you're a healer you should heavily debate the merit of the trinket. Use trinkets I find to be too cool down oriented, and healing I've always found to be too reactive, to make significant use of. If you're the kind of healer that has multiple "oh crap" buttons, you might like it. I tend to rely on pure and simple skill, and forget I even have cool downs until I see single digit percentages.
Now trinkets are your first goal for gearing, since there aren't a ton of them. I will from this point call trial of the champion, pit of saron, forge of souls, and halls of reflections "the new places". These places have very few trinkets for classes, but for the few they do, they're some of the best stuff you'll find. Weapons are good here too. Really anything you find in these instances will outclasses anything you'll find if you haven't been raiding. Don't assume the good stuff is in the heroic mode only either. Regular modes of the new places have been jammed full of loot that while not quite as good as heroic mode, will be the only place you'll be finding stuff. Me personally? I've run regular HoR a crap ton to get "muddied boots of brill" because there simply isn't as good a boot elsewhere.
Like I've said, keep a special eye out for rings, boots, cloaks, trinkets and your weapons (or shields and off hands, you know). Doing this, along with triumph and conquest gear will mean you'll keep your ilvl average at a minimum of 219 (stuff from heroic toc) all the way up to 245 (stuff you actually get from triumph guy, love you triumph guy!)
Now trinkets, once again, are a tricky bunch. You have to get two of them, and the ones from the instances might not be good for you. This is the only time I endorse heroism vendor guy. His trinkets are solid until you find something else you may prefer more. Once again, personally I have the mark of supremacy from triumph guy, and mirror of truth from heroism guy. I could have gotten the needle encrusted scorpion, but armor pen ain't such a hot stat for enhancement shaman, so I passed on it.
Try and research your class about trinkets, and don't trust item levels for them at all. Darkmoon cards are amongst the best trinkets you can find, for instance, but their ilvl 200 is very deceptive.
Don't you just hate trinkets? Yeah me too.