Some requirements:
- Step-by-step debugging & Break Points
- View variable values while debugging
- IntelliSense (auto-completion). Ideally done with "smarts" so it only shows you the syntactically valid options to complete something. E.g., Textbox. would trigger members of that class (.Text, .BackColor), etc. And then Textbox.BackColor= would trigger a list of valid colors.
- Drag'n Drop style GUI design.
I'm not concerned about cost (Ok, over $1K gets a little pricey looking :-)