> I have bi-colour LED's on my board that have about 2.2 volts across
> them when there's 25 mA flowing through them

Tomas, if you look at the spec sheet for the bi-colour you'll see that
each colour has a different forward voltage, Vf. Red is lowest (~1.7V)
and typically Vf rises as you go up the rainbow through yellow, orange,
green, blue, to white. Green also typically uses more power than red
for the same perceived brightness. Before getting very specific about
other components, you really should sort out what colour LEDs and
what style (standard, diffused, water-clear, superbright, ultrabright etc)
are going to be in the final product. To make that decision you are
going to have to get stuck into LED data sheets

> I'm thinking of using a single 1.5 volt AA battery to power my
> board

> 1) Can I go straight from the 1.5 V battery into the LED's without
> a current-limiting resistor?

You can, but if Vf is higher than Vbatt, and it is, the LED will not light

> 2) What kind of regulator should I use to provide my uC with
> 5 volts?

If you're converting an AA to 5V, then you'll need a boost circuit,
and obviously the higher the conversion efficiency the better as
the AA is a limited reserve of power

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