The GNOME Canvas

Structured graphics
Hierarchical organization of items
Can create objects and refer to them later
Canvas items
High-level API
Automatic event handling
Fully integrated with the GTK+ object system
Goodies
Unlimited scrolling
Look, Ma, no flicker!
Generic display engine
Extensibility through custom items
Gnumeric, Gnomecal, Achtung, EZPaint