Core only build

[fulong]

We are starting at level 5 and are allowed all MMs and PHB1 +2 and DMG. What are some great builds?

[Kremlin K.O.A.]

Easy Mode:

Druid
Max out wisdom, DW about str or dex.

Take mostly utility and support spells.

Use Wild shape for some combats then switch out to being a support caster for the rest

At next level get natural spell and stay in Wild shape most of the time.

Now for a more specific answer, what are the rest of the players playing?

[Nanashi]

Aside from straight full caster (+DMG prcs), Bard and Duskblade (and maybe Warforged Barbarian, since they're in MM3), the best build in your limits is likely Horizon Tripper (dip Fighter, Ranger and Barbarian to qualify for Horizon Walker and abuse that sweet all day teleportation)

[Hades]

I second a druid for "easy mode".

If you like to focus on summoning, you can simply pick Spell Focus (conjuration) & Augment Summoning, then when you hit 6th level Natural Spell and stay in Wild Shape.

[Kremlin K.O.A.]

To create the aggressively hegemonizing ursine swarm,.

[Keldar]

To create the aggressively hegemonizing ursine swarm,.

Bears, a theme for the whole party.  Bear summoning Druid with bear companion, Celestial Bear summoning Conjurer, Bearbearian. 
And the rogue Zoidberg.  ...Riding a bear.
Pity Ursinal didn't make it into an MM from the BOED.

Incidentally, the PHB 2 inclusion begs the question: Can you use the classes that get alternate class features in PHB2 that aren't in either PHB?