The Witcher

[FactionHeir]

I've been reading up on it some and the expansion (or rather the Enhanced Edition) is available for free for those who already have registered their game on their website. You'll be notified when its available and can then download it from there directly.
A list of things that will be included in the EE in addition to bugfixes and longer, more fleshed out dialogue:

Extra music/soundtracks
Improved inventory:
o Filtering of alchemy ingredients by content,
o Auto-sorting of items in satchel,
o Special slot area for sorting alchemy ingredients in satchel
Auto-save option (on/off).
Character differentiation mechanism (effectively generating
approximately 50 new character appearances).
Look-at feature (characters look at Geralt, deepening player
immersion).
Auto-looting of containers (player may collect all contents of a
container without opening the container panel).

Oh, and it'll be released 1st half of September.

Source: EE Fact sheet (slightly outdated, but all relevant)