Midsummer Fun: Desecrating the Flames
The quickest, easiest way to make gold and Burning Blossoms in the Midsummer Fire Festival is to tour the worlds, stopping at each of the flames and bonfires, both Horde and Alliance. There are many of these locations, both on Azeroth and Draenor. Honoring a flame of the same faction nets you 5 gold, 95 silver, and 5 Burning Blossoms. Desecrating and extinguishing the opposing faction's bonfires earns you 11 gold, 99 silver, and 10 Burning Blossoms.
Be warned, desecrating a bonfire flags you for PvP, if you are not on a PvP server. Both on PvP and PvE realms, expect many of these sites to turn into warzones. You can expect the worst of this action to be near the neutral Goblin towns such as Booty Bay and Gadgetzan. The flames are practically right next to eachother, so battles for dominance are inevitable.
Scouring the entirety of Azeroth and Outland for these flames can be a bit of a task, so we did it for you! A list of all of the bonfire locations are below, with the settlement they are closest to listed. They are all more or less in the direct vicinity of the Horde, Alliance, or Neutral town mentioned.
The easiest way to complete this is to start at one end of the continent, either far north or far south, and work your way up/down zone by zone. While you're doing this, you can also pop into the various opposing enemy cities to begin A Thief's Reward.
Horde Fires
Stonebreaker Hold, Terokkar Forest
Shadowmoon Village, Shadowmoon Valley
Garadar, Nagrand
Zabra'jin, Zangarmarsh
Thunderlord Stronghold, Blade's Edge Mountains
Thrallmar, Hellfire Peninsula
Stonard, Swamp of Sorrows
Flame Crest, Burning Steppes
Kargath, Badlands
Hammerfall, Arathi Highlands
Tarren Mill, Hillsbrad
Revantusk Village, Hinterlands
Sepulcher, Silverpine Forest
Brill, Tirisfal Glades
Tranquillien, Ghostlands
Falconwing Square, Eversong Woods
Razor Hill, Durotar
The Crossroads, The Barrens
Sun Rock Retreat, Stonetalon Mountains
Shadowprey Village, Desolace
Splintertree Outpost, Ashenvale
Brackenwall Village, Dustwallow Marsh
Bloodhoof Village, Mulgore
Freewind Post, Thousand Needles
Camp Mojache, Feralas
Alliance Fires
Allerian Stronghold, Terokkar Forest
Wildhammer Stronghold, Shadowmoon Valley
Telaar, Nagrand
Telredor, Zangarmarsh
Sylvanaar, Blade's Edge Mountains
Honor Hold, Hellfire Peninsula
Nethergarde Keep, Blasted Lands
Darkshire, Duskwood
Sentinel Hill, Westfall
Goldshire, Elwynn Forest
Lakeshire, Redridge
Morgan's Vigil, Burning Steppes
Thelsamar, Loch Modan
Kharanos, Dun Morogh
Menethil Harbor, Wetlands
Refuge Pointe, Arathi Highlands
Southshore, Hillsbrad
Aerie Peak, Hinterlands
Chillwind Camp, West Plaguelands
Nijel's Point, Desolace
Astranaar, Ashenvale
Auberdine, Darkshore
Dolanaar, Teldrassil
Azure Watch, Azuremyst
Blood Watch, Bloodmyst
Theramore Isle, Dustwallow Marsh
Feathermoon Stronghold, Feralas
Neutral Towns with Alliance and Horde Fires
Area 52, Netherstorm
Everlook, Winterspring
Booty Bay, Stranglethorn Vale
Cenarion Hold, Silithus
Gadgetzan, Tanaris
In addition to the material bonus that comes with desecrating the opposing faction's flames, don't forget that you have good reason to keep your own faction's flames burning! Keeping that flame alive provides a really nice buff that you ought to take advantage of, or at least help your fellow member of the Horde/Alliance by preserving that buff for them. Is it worth fighting tooth and nail for? That's up to you to decide!
Update: Reader Elory has made a checklist using this information and some additional information provided by our other readers. It's formatted for easy printing, and you can check off the ones you've already done as you go. Thanks, Elory!