After all, I ended up on LXDE shipped by Lubuntu 12.04. It looks really nice, the default theme is perfect (unlike that of Xubuntu).
One tricky thing is though how to add a keyboard layout on Lubuntu 12.04 (if you didn't specify an additional language at installation). Basically, I consider a lack of a working GUI (lxkeymap returns an error) to configure keyboard layouts a big flaw of LXDE (there are other ways to configure this aspect of LXDE of course, I'm just saying no GUI is bad).
So here is what I did to add a new keyboard layout.
1) Add a layout indicator to the panel - right click on the panel - Add / remove panel items - Panel Applets - Add - Keyboard Layout Switcher.
A switcher will be added to the panel, in Panel Applets you can choose the position for the switcher you like.
2) Next is to add a new layout. For example, I need Russian. This will be done by editing a configuration file. Run:
gksu leafpad /etc/xdg/lxsession/LXDE/autostart
Enter your administrative password to open up the document with root privileges. Then find the line @lxpanel --profile Lubuntu and add the following:
@setxkbmap -option grp:switch,grp:alt_shift_toggle,grp_led:scroll us,ru
Save file. Logout, login.
Press alt+shift to see whether the layout changes or not. It should change :)
By the way, there are more ways to add a layout on LXDE. They're nicely listed in this document:
How to change layout switch shortcut on Lubuntu 12.04
Examine the line - @setxkbmap -option grp:switch,grp:alt_shift_toggle,grp_led:scroll us,ru
What you need is "grp:alt_shift_toggle". Replace alt_shift with alt_ctrl, for example.