In Mac OS X, it's easy to find those symbols that you want but just don't know how to get!  You need to use either the Character Viewer or the Keyboard Viewer.  To do this, you need to display them in the menu bar.  This may be disabled by default, in which case you should go to the Apple Menu and choose System Preferences.  Then look for Language & Text and when that pane appears, look for the tabs along the top.  Click the Input Sources tab and you will see the following:


Make sure to switch on Keyboard & Character Viewer.  This will display a little icon in the menu bar which you can click to access the Keyboard & Character Viewer.  It looks like this:


Now, you can select Character Viewer from the menu and the following window will appear:


Here, you can find all sorts of symbols just by looking through them and when you find the one you want, you can drag and drop it straight into the document where you need it.  This is easier than having to know key combinations, but takes longer.  You can also use the Keyboard Viewer, which is a very handy tool and looks like this:


Basically, this is a representation of your physical keyboard and as you press modifier keys on your keyboard, the symbols on the keys change accordingly.  If you hold down the Shift key for example, all the letters will turn to uppercase.  This allows you to see exactly which symbols will be produced with what combination of keys.  If you tend to write in foreign languages, this feature can be particularly useful.