Excalibur 2.0 Beta:
Meta Editor with Real Time Halo support

Also has support for hot keys:
ctrl + O: Open a map
ctrl + R: Resign the open map
ctrl + M: Show/Hide the tags TreeView
ctrl + S: Save changes to meta
ctrl + alt + S: Sync to xbox

To use RTH you need to get your xbox's debug IP address.
Put the Debug Address in the TextBox and click connect, you will be notified when you are connected
Then edit the meta that you want to play with and click save and then click sync
Remember you can press control + S and then control + alt + S to do the last step