I've seen Sigur Ros before and I'd say go see Isis and Dalek. That show will be much better. Sigur Ros' drummer was so sloppy and his time was so all over the place that it distracted from the music to the point where it wasn't actually enjoyable to listen to. The only member of the band who was *really* on top of things was the singer (who was awesome). Isis and Dalek, on the other hand, kick ass live.
OK, I'm buying tickets tomorrow--I hope they're not sold out. Fusoya, if you wanna buy them today (I'm working 9am-12:30am, so I don't have time), get an extra one for Tom.