What LED driver IC options do I have to build a two-cell driver for a 3 W LED?
You didn't specify the forward voltage on the LEDs, which makes a huge difference. Since two rechargeable AA batteries in series will have an open circuit voltage of 2.4V, if your LED(s) has a Vf above that then you may need to use a different solution than if it is below. HBLEDs have a high Vf; for a 3W LED a Vf of 3.5V or higher is normal.

So, if you have a supply voltage of 2.4V from the AAs, and a Vf of 3.5V for the LEDs, then you will need an LED driver IC that is a boost converter like the LT1618. Or make your own, but it's much easier to just buy one; there are many out there. Generally these are more of a pain than buck converter drivers. If you want to make your design easier, then add another AA battery so that your supply voltage is 3.6V; then you can use an easier buck converter IC.

As for which IC is best, there are many options out there, from vendors like TI, National Semi, etc.