We recently played through the Red Hand of Doom and my Binder was the only one to survive the entire game. Dhalver-Nar was indispensable for the dragon fights, with a high Bluff and Diplomacy score from Naberous to fool them into thinking that if my character died, the dragon would as well. Saved the party from a TPK at one point as they decided to take prisoners instead of simply killing us.
I'll have to write up my full list of all things Zceryll can be used for with a list of the summons I found most useful as well. I have a mostly completed list of stat blocks for all legal summon monsters with the pseudonatural template added, a list of all plant materials the Djinn can summon from the books, as well as some calculations on size and value for each casting. I'll have to complete it, but once I do I'll send it along to be posted.
Some fun additions from Naberous's Skills - choose whatever language you might need for the day with his skill option, lucid dreaming can also be fun if you can get a way to boost the skill check high enough to get a 25 reliably, use it to become Freddy Krueger to your enemies (page 203 in the Manual of the Planes) or to just communicate long distances with anyone.
A Lyre of Building, combined with wooden supplies from Zceryll can get you a 68571gp stronghold built once per week, with just 8 hours of playing. All of this done, for free. My character's bard cohort makes the perform checks for him. He's currently using this ability to rebuild Drellan's Ferry and start a stronghold of his own for the area. Eventually he'll use it to build an airship and just have to pay to have it enchanted.
If you just need weapons or armor a Djinn with its +12 Craft check can take 10 to make 1 masterwork Bronze wood item every 30 seconds for as long as you can keep summoning them.
Djinn also get Airwalk 1/day, with a Caster Level of 20, so each summon can grant 6 creatures the ability to use the spell. Our party was using it toward the end of the campaign to fly at 60mph in streams of white smoke like slow motion versions of the Death Eaters from the Harry Potter movies, takes 5 rounds to switch from smoke to solid form.
One thing I wasn't sure of, Summons can't use their teleportation or summoning Spell like abilities according to the summoning school, does that also include Plane shift if not once you get to Summon monster VII you effectively have a teleport as well, just plane shift to a benign plane (astral, celestial, ethereal), then again back to your destination on the material plane.