Here's some very handy commands. I use most, if not all, of these on a regular basis.
$ namei -m /var/log/httpd/error.log
f: /var/log/httpd/error.log
drwxr-xr-x /
drwxr-xr-x var
drwxr-xr-x log
drwxr-xr-x httpd
-rw-r--r-- error.log

Substitute a string in a variable in bash.
$ version="6.4.4-5"
$ echo ${version%%-[0-9]*}
6.4.4

Exclude all the .svn files in a find, and look for a pattern in the results.

find $1 -name '.svn' -prune -o -print | xargs grep -l "$2"

Perl oneliner to convert an epoch to the current date/time.

perl -le 'print scalar(localtime("1223234245"))'

I also started doing a lot of work in Ruby last year after hearing about, and deploying at the company I worked for, a configuration management tool called Puppet. Along with Ruby scripting, I've come to love two excellent tools: rake and capistrano. The quick version, rake is a "make" for Ruby. It will execute shell commands and can do all kinds of awesome. Capistrano was originally written to aid in deploying Rails applications on multiple systems, and has also become a sort of glorified "ssh for loop" since it uses Ruby's Net::SSH class.

Don't set up ssh keys without passphrases unless absolutely necessary*. Use an ssh-agent to store the private keys. There's automated methods for this on every major platform.

• Linux, ssh-agent and ssh-add. The man pages are complete, and automating this is easy in the shell. Alternately GNOME users can use Seahorse to tie the ssh keys into the login keychain.
• Mac OS X, ditto ssh-agent/ssh-add, or use SSHKeychain.app, which will add the keys and passphrase to the login keychain as well.
• Windows, if you're using SSH on Windows, its puTTY, and you should already have the putty agent installed from the installer. You used the installer right?

*Necessary would be for automated application processes that need to ssh to systems without user intervention.