A guy on the Sneap forum has made this big bundle of impulses that sound way, way better than a lot of impulses I've heard. He's uploaded a demo with just under 30 impulses for free, while the full version will be $40.
Lots of clips here Recabinet - Album quality guitar tone, direct. Media
and you can read about it here Recabinet - Speaker Simulation for Guitar and Bass - Convolution Impulse Response Technology and here Recabinet - Ultimate Metal Forum with the demo download link on either 6th or 7th page.
This clip was great http://recabi.net/mp3/lord_awesomeguy_recabinet.mp3 and this one is also very good http://recabi.net/mp3/GrooveMetal_FullMix.mp3
Yeah, he's been talking about it for a while. I'm not sure how I feel about him charging $40 for impulses, but I would like to try it out and hear a bit about what it is exactly that he does differently.