Yeah, both the NiMh and Lithiums are pricey compared to Alkaline and NiCd.

For your wireless mouse I'd say go with either NiCd or Lithiums. Lithiums will have a longer life (higher energy density & very low self discharge) but NiCd's would do as well. I can't seem to find rechargable Lithiums in a AA package. I'd avoid NiMH as you'd be charging them almost bi-weekly due to their self discharge characteristics.

Panasonic batteries (NiCd, Alkaline and NiMH) are available through Digi-Key, but they don't carry chargers. Walmart has a pretty good selection of chargers for AA's, but be sure to match to the battery type/chemistry. Energizer makes a AA Lithium that's available through Mouser 525-L91BP-2 for $5.81 for 2, but it's not rechargable.

Oh yeah, avoid 'Heavy Duty' (Zinc Chloride and Carbon Zinc) batteries. They have a very low energy density (ie they die butt fast).

-Zeke