Windows Live Hotmail is a web-based email provider by Microsoft that will eventually replace the old MSN Hotmail once it is complete.
Along with features like drag-and-drop, a configurable reading pane, spellcheck-as-you-type, and a customizable look-and-feel, it has a growing set of keyboard shortcuts.
|Enter||Open selected message in full view|
|Delete||Delete selected message|
|Esc||Return to inbox|
|]||Next contact (when viewing contacts)|
|[||Previous contact (when viewing contacts)|
If you're wondering, I do happen to work on the Windows Live Hotmail team.
As such, here are my shameless extra links related to the product =]