Pets and Vanity Items:
Brazier of Dancing Flames: This baby costs 350 Burning Blossoms, but it's probably worth it. When you right click it, it will summon a Brazier with a dancing female Draenei made of pure flame. How awesome is that? It actually gets more awesome, since she reacts to emotes, including /kiss, /bow, /wave, and /silly. Also, you'll definitely want to /dance with her. If you do, you'll get a buff that will turn you into a firedancer just like her! If you buy only one thing this midsummer, this is probably what you want.
Captured Flame: In previous years, this pet was the reward from A Light in Dark Places, which required you to visit various old world dungeons. That quest is now completely defunct, but you can still get the pet by shelling out 350 Burning Blossoms. The pet itself looks a bit like a red or pink tinted wisp.
Mantle of the Fire Festival: In previous years, this mantle was a reward from the quest Wild Fires in the Eastern Kingdoms. That quest is now defunct, but you can buy the mantle for 100 Burning Blossoms. It looks like a pair of braziers perched on your shoulders. There are no dancing Draenei girls attached to these ones, though.
Vestment of Summer: This simple robe is purchased for 100 Burning Blossoms. It looks pretty nice, but what's also fun is the right click. When you use the robe, you'll begin to dance with your hands wreathed with fire, like you were casting a fire spell.
Sandals of Summer: Despite the fact that they're less noticeable than the vestments, these cost 200 Burning Blossoms. When used, they create a fire beneath your feet. Luckily, it's okay to stand in these flames. The effects of the sandals and the vestment can be combined for the penultimate in Fire Festival hotness (the ultimate still goes to the Draenei firedancer, of course).
Stat Buff Items: There's a whole bunch of "food" from the Festival as usual. In past festivals, you could only get it from certain quests, but now you can spend your Burning Blossoms for it. Despite having food-like names, they're on use items, so the buffs will stack with food buffs. They'll expire 14 days from date or purchase, so be aware of that as well. All of these items cost 5 blossoms for 5 pieces, except for Midsummer Sausages, which cost 5 blossoms each. The buffs are as follows:
You can also get a Bag of Smorc Ingredients, but it doesn't seem to have much advantage over buying the Toasted Smorcs directly. It costs the same as the Smorcs themselves, and needs a cooking fire to be made into Smorcs. Maybe it's a Roleplaying nod.
Handful of Summer Petals: These act more or less like the Handful of Rose Petals from Love is in the Air. Throw them at someone, and they'll get a nice shower of flower petals for a few minutes. These expire in 10 days of the date of purchase, so watch out for that. 2 blossoms get you one handful of petals.
Juggling Torch: These will only show up on the Vendor once you've completed the Torch Catching quest. Apparently you have to be certified before they let you play with fire! They act more or less like the torches from the Torch Catching quest, except you can throw them to other people too - assuming those people are also certified torch jugglers. 5 torches will cost you 5 blossoms.
Fiery Festival Brew: Drink these, and you'll belch out a nice stream of fire from your mouth for a few seconds. Great for impressing that hot dragon chick you've wanted to ask out! Be warned that it now has an expiration time of 14 days, unlike it in past years. 2 blossoms will net you 5 brews.
You've probably noticed by now that you'll need to spend a whole lot of blossoms to get all these goodies. Luckily, you have our quest guides to help you get them. Still, it's probably a good idea to carefully prioritize your purchases. Even with the dailies and all the fire desecrating, you may find yourself short on funds if you blow everything on Juggling Torches and Fiery Festival Brew, especially if you miss a few days of dailies. Good luck on the blossom gathering, and I hope you manage to buy all the stuff you want!