Drush command to show aliases?
You can use this in the terminal 

drush sa


For example on my dev server:

- drush sa
@8080
@commons_3_dev
@none
@w2


The aliases are set in file called aliases.drushrc.php. For me this is located in /usr/local/share/drush/. Depending on how you installed Drush and on which distro you're on this may differ.

You can set up aliases in this fashion inside that file

$aliases['8080'] = array(
'uri'=&gt;'server.com:8080',
'root'=&gt;'/var/www/html_webtest2',
);

$aliases['w2'] = array(
'uri'=&gt;'webtest2.server.com.edu',
'root'=&gt;'/var/www/html_webtest2',
);

$aliases['commons_3_dev'] = array(
'uri'=&gt;'yourserver.com/c3d7/',
'root'=&gt;'/var/www/html_commons_3_dev',
);


For more fun, you can chain these together for server wide backups. For example, I do a big back up to all aliased sites like this

 drush sa | egrep "(@|default)" | egrep -v "(@none|@self) | xargs -L1 drush arb


Taken individually

 drush sa  # list site aliases
 | egrep "(@|default)"  # include default and any line containing a @ mark
 | egrep -v "(@none|@self)" # remove any lines with @none or @self 
 | xargs -L1 drush arb # with each line run drush archive-backup


To find path and other info, use a bit o' pipping:

drush sa | xargs -I {}  sh -c "echo {}; drush {} st"


To narrow it down to finding paths:

    drush sa | xargs -I {}  sh -c "echo {}; drush {} st" | egrep "(@|path)"
@8080
 Site path                     :  sites/8080.webtest2               
 File directory path           :  sites/8080.webtest2/files         
 Private file directory path   :  /var/www/drupal_private_files                   
@commons_3_dev
 Site path              :  sites/default                                          
 File directory path    :  sites/default/files                                    
@none
@w2
 Site path              :  sites/default                                          
 File directory path    :  sites/default/files 


update

A bit late but I wanted to say don't forget about drush @sites st. I believe the @sites parameter will act on everything found under the sites folder. Think 

drush @sites cron -y # runs cron on each root/sites/site
drush @sites rf