The LD12 seems to be a great light. I was considering buying it myself a couple of months ago and went for the LD10 instead because I mind the twist heads rather than head switch.
The LD12 does have a few improvements on the LD10: besides runtime, the forward clicky and the memory definitely come in handy.
If you want diffusers for the LD12, you have plenty of choice: transparent white diffuser cone, red diffuser cone, flip-up diffuser, red filter, traffic wand! Actually there is an accessory set that came out at the end of 2010 that is great value: it includes the transparent the white diffuser cone, the flip-up white diffuser, the red filter, and the traffic wand and it should sell for around $10. I think I saw it still in stock on Amazon not long ago!
If you want something to carry batteries you can just buy a PowerPax or a Batuca battery case: they carry four batteries though.