geany is definetly missing a debugger(interface).
Though there exists a plugin called geanydbg as an integrated frontend for gdb, it is not in the repositories and compiling it oneself gives quite some problems (gtk+-2 bla bla), here is how to get it working (without compiling anything):
1. make sure gdb (the actual debugger) is installed
2. upgrade geany to 0.17(-1) through the debian unstable repository
3. download geanydbg plugin from here: http://ftp.cica.es/ubuntu/ubuntu/pool/universe/g/geanygdb/geany-plugin-gdb_0.0.2-0ubuntu1_i386.deb (of course depending on your architecture)
4. goto to folder it has been downloaded and install it by: $ sudo dpkg -i geany-plugin-gdb_0.0.2-0ubuntu1_i386.deb
Now a debugger panel is available next to the "Documents" and "Symbols" Tabs
