A tidbit of very useful information (hope rsg guys don't mind, it took me days to figure this out, why not help the next newbie).

Some 3rd party modules do not have the option for their own custom css styling. Their edit panel does not show "Assign Module class suffix". With help from joomla.org forum here are the instructions on how to do this.

 
1. Open the module's xml file (modulexxx.xml) from the module directory joomla\modules.
 
2. It should have something like this inside:
 
 
<?xml version="1.0" ?>
<mosinstall type="module">
<name>Weather DirBG</name>
<creationDate>06/30/2005</creationDate>
<author>Ivan Kostov</author>
<copyright>This component in released under the GNU/GPL License</copyright>
<authorEmail>chessko@gmail.com</authorEmail>
<authorUrl>www.mambo-bg.com</authorUrl>
<version>1.0</version>
<description>Module displays a weather powered by dir.bg.</description>
<files>
<filename module="mod_weatherdirbg">mod_weatherdirbg.php</filename>
</files>

[Right here is the correct place to add the assign class code! Notice </files> above and </mosinstall> below]
 
</mosinstall>
 
 
 
3. This is the code to add, all of it:
 
<params>
    <param name="moduleclass_sfx" type="text" default=""
           label="Module Class Suffix"
           description="A suffix to be applied to the css class of the module
                       (table.moduletable), this allows individual module styling" />
    <param name="@spacer" type="spacer" default="" label="" description="" />
    <param name="ordering" type="list" default="hits" label="Back Button"
           description="Show/Hide a Back Button, that returns you to the previously
                        view page">
      <option value="hits">Hits</option>
      <option value="title">Title</option>
    </param>
  </params>

4.Save the file and now in the edit panel of the module you have the assign class suffix option. An option to show a 'back' button appears as well (code is taken from joomla.org developer manual), I could not get it to work without that line.
 
Good luck to all!
Mariya