Brynju Thunderclap was the last tower boss I had yet to try. Since this was my first time, I cleared the whole room and fought him on his platform to avoid any chance of getting adds.
My team:
65 Monk 746 AA + DPS Merc
65 Shaman 837 AA + Healer Merc
65 Ranger 85 AA + Tank Merc
The main issue I've had with the tower bosses is the Healer Merc running out of mana. I finally found a way to control that and now the Healer Merc will have 20-80% mana left at the end of a tower boss fight. What I do is pretty simple but it works great.
When I start the fight, I make sure boss is slowed then I put my Healer Merc on Passive. I watch the tank's health and when it reaches around 40%, I put my healer merc back on Efficient and it will immediately cast a Complete Heal. I put the merc back on Passive and repeat this process.
Here's the slightly tricky part, if the boss gets a few good shots on your tank, his HP might get too low by the time the CH is done and the Healer merc will start casting Holy Elixir and Supernal Remedy several times instead. This will drive your healer Merc OOM especially as she will also cast group heals and similar spells to keep the rest of the group up. So what I do is I throw a heal or 2 on the tank with the shaman to keep him above 30% HP or so until the CH lands and then put the healer back on passive. To deal with group damage from AE, rampages etc. I just throw the Shaman's Call of the Ancient ward on the floor which lasts a quite a while and I'll cast a couple of heals here and there to keep everyone up. The highest I could get Call of the Ancient AA at level 65 was rank 5/8 and I think it heals for around 300 HP per tick with some stats increases which is just enough to keep my party up.
These fights have taken about 5-10 minutes for my group. This time, Brynju Thunderclap dropped a spectral parchment, the usual 10-slot ring container and 2 Ornate Chain Tunic patterns.
Edited, Sep 24th 2011 4:45pm by Gastank

Blue Diamond
Brick of Ethereal Energy
Cap of Drowned Souls
Fungus Clump
Glowing Orb of the Stormwatcher
Glyphed Rune Word
Legends of Norrath: Forsworn Booster Pack
Lightning Encased Signet
Orb of Electricity
Ornate Chain Tunic Pattern
Peridot
Shard of Pure Energy
Strand of Ether
Unadorned Symbol of Torden
Wicked Shank