Intuitive GUI interface
The usual debugging operations (step-into/step-over/run/break)
Conditional breakpoints
Debugging core is implemented as a plugin so people can have drop in replacements. Of course if a given platform has several debugging APIs available, then you may have a plugin that implements any of them.
Basic instruction analysis
View/Dump memory regions
Effective address inspection
The data dump view is tabbed, allowing you to have several views of memory open at the same time and quickly switch between them.
Importing of symbol maps
Plugins
Search for binary strings
Code Bookmarks
Breakpoint management
Check for updates
Environment variable viewer
Heap block enumeration
Opcode search engine plugin has basic functionality (similar to msfelfscan/msfpescan)
Open file enumeration
Reference finder
String searching (like strings command in *nix)
Hardware Breakpoints
http://www.codef00.com/projects.php#Debugger