Switch to an app named (start it if needed) or toggle between its windows. Could be assigned to hotkey. Got it here - http://somanov.wordpress.com/2009/12/02/window-shortcuts-for-linux-desktops/

activate_app.py

#!/usr/bin/env python
import os
import sys
import commands

program_name = sys.argv[1] # the program to be focused

# get all windows which contain "program_name" from wmcontrol
candidates = sorted([x.strip() for x in commands.getoutput(""" wmctrl -l -x | awk -v win="%s" 'tolower($0) ~ win {print $1;}' """ % (program_name, )).split("\n") if x !=''])

if candidates: # at least one candidate found , we need to check if the active window is among the candidates (for cycling)
    # Get the id of the active window

    # Note: wmctrl currently does not support getting information about the active window.  In order to realize this
    #       we use xprop here. Unfortunately xprop gives us the window id of the active window in a different format:
    #       Window ids from wmctrl always begin with 0x followed by 8 digits (leading zeroes for padding). xprop
    #       does not do the padding and might give a window id starting with 0x followed by only 6 digits. The
    #       lines below get the id of the current window and make the id returned by xprop comaptible with
    #       the window ids returned by wmctrl.
    active_window_string = commands.getoutput("""xprop -root | grep "_NET_ACTIVE_WINDOW(WINDOW)" """)
    active_window_string =  active_window_string[active_window_string.find("#")+4:].strip()
    active_window = "0x" + "0" * (8-len(active_window_string)) + active_window_string

    next_window = None # the window to display. (one of the windows in candidates)
    if active_window not in candidates: # if the active window is not among the candidate windows
        next_window = candidates[0] # ..just show the first candidate window
    else: # we are already showing one of the candidate windows
        next_window = candidates[(candidates.index(active_window)+1) % len(candidates)] # show the *next* candidate in the list (cycling)

    if next_window:
        os.system(""" wmctrl -i -a "%s" """ % (next_window,) ) # tell wmcontrol to display the next_window
else : # no windows open which fit the pattern of program_name
    os.system("%s &" % (program_name,)) # open new window