http://ihackernews.com/ is an excellent Hacker News mobile website. It also provides the third-party Hacker News API used by Combinator.

The problem is that Windows Phone doesn't allow users to pin website icons to their start screen (you can pin a static web page preview but it doesn't look very good). Fortunately, http://www.web2tile.com solves this issue, but not enough people are aware it exists. I may try to build a native app for it, but I'm not sure Microsoft would allow it.