We've been using naturplus which was one of the cheaper wallpapers but it's also really green too! It's made completely of recycled paper, and doesn't contain any plastics or vinyls. It's hypo-allergenic too which is reassuring after all the dust we've been creating with other work.
It's lovely to find eco products that are similar in price (or cheaper!) than conventional ones and also right next to each other on the shelves, rather than off in some separate green section. Another sign that being green is becoming more and more mainstream.