There's a site with quite a handful of pretty skins for the native keyboard, dialpad and today themes for Windows Mobile 5.0. I'm not sure how well some of them work with older OS.
Too bad these do not work on WM2003. I've been using the skin in Tweaks2k2 for WM2003 for quite some time...and I nearly forgot how the original keyboard looks like.
According to buzzdev, we need to have certification removed (nocert WM5.0) for the keyboard skins to work. I had them on my xda2, and I miss them on my Dopod 818pro...