Try OmniGraffle with Nisus Writer Express
Omni just released the beta of OmniGraffle 4. Aside from its nifty new palette system, it also supports LinkBack so you can edit OmniGraffle drawings in your Nisus Writer Express documents with just a double-click. To try it out get the OmniGraffle Beta the latest preview release of Nisus Writer Express 2.5. It’s awesome!