I think the character optimization boards don't talk about party optimization much since most of the characters they build are designed not to need a party (or if they do, they just need an abstract Tactical Warlord giving them a buff for their uber combo).
As far as actual party synergies go, another is sustainable/persistent harmful zones and push/slide powers. At level 1 you can have Flaming Sphere + Tide of Iron off the top of my head. A Warlock + a Wizard focusing on zones (so they have enough of them to drop one or more most fights during the day) and push powers alone would be pretty powerful and if everyone else picked up an encounter and/or at-will that pushed or slid...
There's a million little synergies that can work too, like a melee cleric with Righteous Brand + any other melee character readying their action for when the cleric attacks so they can get two rounds-worth of attacks with the cleric's bonus. Or (assuming your DM interprets it favorably) having a bard with misdirecting mark + an assault Swordmage, so they have to Aegis targets each round.