arcpy - Listing all feature classes in File Geodatabase, including within feature datasets?

From python how can I build a list of all feature classes in a file geodatabase (*.gdb), including inside feature datasets? The standard example only lists feature classes at the top level of the geodatabase:

import arcgisscripting, os
gp = arcgisscripting.create(9.3)

gp.workspace = 'd:\scratch.gdb'
fcs = gp.ListFeatureClasses()

for fc in fcs:
    print fc

Please indicate which ArcGIS Desktop version your answer applies to (I am looking for 9.3 but we might as well collect all versions in one place).

Answer

I ended up using gotchula's answer, but without yield because I generally re-use the FC handles created and yield's are used once then discarded it's easier for me to read and understand what fcs.append() is doing than fcs = yield(...).

def listFcsInGDB(gdb):
    ''' list all Feature Classes in a geodatabase, including inside Feature Datasets '''
    arcpy.env.workspace = gdb
    print 'Processing ', arcpy.env.workspace

    fcs = []
    for fds in arcpy.ListDatasets('','feature') + ['']:
        for fc in arcpy.ListFeatureClasses('','',fds):

            #yield os.path.join(fds, fc)
            fcs.append(os.path.join(fds, fc))
    return fcs

gdb = sys.argv [1]
fcs = listFcsInGDB(gdb)
for fc in fcs:
    print fc            

Results:

d:\> python list-all-fc.py r:\v5\YT_Canvec.gdb
Processing  r:\v5\YT_Canvec.gdb
Buildings_and_structures\BS_2530009_0
Buildings_and_structures\BS_2380009_2
Buildings_and_structures\Tower
Buildings_and_structures\Underground_reservoir
...

This is now in a module I call arcplus*. Place with your other code or PYTHONPATH and then:

import arcplus

fcs = arcplus.listAllFeatureClasses('d:\default.gdb')
for fc in fcs:
    print "magic happens with: ", fc

Arcplus also adds wildcard filtering; to process only feature classes that start with "HD_" within feature datasets containing "Hydro"

fcs = arcplus.listAllFeatureClasses(gdb, fd_filter='*Hydro*', fc_filter='HD_*')

.* now on Github, upgraded for 10.x. For arcgis 9.3 see here.