mikedocy
Put Voxengo Span on your master buss or any track and get real-time RMS readout.
It's free:
http://www.voxengo.com/product/span/

I actually already do...hence my work sounds alright...I've just worked how bad my ADHD is or arrogance...take your pick. Mix of,last track if you can call it that was not great because I finished composing the thing then actually didn't mix it properly timing errors and over compression. Shakes head. 
 
Ben

Mikedocy - I just found SPAN and was coming back here to report out on it - works for my purposes.  Thanks!
 
For what it's worth - I think -18db is fine for a classical song.  Especially if it's a mellower song.  I've looked around a lot at the RMS levels of recordings and many Jazz and Classical songs are around that range.  Pop gets up to -14db.  Bad Pop gets a little bit higher.  Metal might reach a little bit higher.  But to me that all sounds way too loud anyway.
 
I make a lot of Funk stuff and I try to hang out around -16db.  That's fine for me.  
 
But I think it all boils down to what sounds good to you.

You might look at this.  Its cool and free.
 
http://www.orban.com/meter/

BretB
You might look at this.  Its cool and free.
http://www.orban.com/meter/

 
Thanks for this.
 
Here's a free vst plugin Klangfreund LUFS Meter that I just stumbled across.

I use and like the Orban loudness meter. But it works a bit differently to a standard plugin concept.  You have to route audio to it.  It can be tricky but my PatchMix software for the EMU audio interface I use allows some pretty fancy routing so I can do it.  You may have issues getting it to work.
 
The Klangfreund meter is good and works just like a normal plugin and can be inserted anywhere.
 
 

So if I understand correctly (not likely) my mastered material, if at a -1.0 dB (SSL) is really too loud?