HL2 didn't seem to provide us with a new fade texture, but there is a pretty cool effect you can use there that's not too performance-heavy and it looks really nice - Make a brush with any non-trigger/nodraw texture on it, tie it to a func_dustmotes, and mess with the color and particle size - this will put some little specks of dust floating around where the brush is, and it looks very cool.
There's a vol light model in the effects folder you can use for volumetric lighting, but the func_dustmotes, or a func_dustcloud entity, is probably a bit easier to use.