Edit: Unfortunately, the images originally included in this post are gone, because of hosting problems in late 2009. My apologies.
I didn’t think such an animal existed, but here it is — Sakura.
Follows your GTK theme, has a nice right-click menu and copies and pastes like a text editor. Pseudotransparency, customizable backgrounds and excellent font effects. It’s just about perfect. This might be the end of rxvt-unicode for me.
That’s the Arch version, by the way. Ubuntu users will need to compile from scratch.