During SharpDevelop developer days 2009 we implemented new debugger features to appear in SharpDevelop 4:

Debugger tooltips for IEnumerable

The individual items of IEnumerable can be expanded normally.

Text visualizer

There is a new visualizer chooser in debugger tooltips.

For string values, Text and XML visualizers are available. Choosing "Text visualizer" shows a window:

XML visualizer

XML visualizer uses AvalonEdit to display syntax-highlighted xml. Folding (= node expanding/collapsing) and auto indentation will be implemented.