MakeShift
Limiter No. 6

+1

Sanderxpander
I hear Limiter6 is pretty good, it's free. It won the KVR plugin challenge some years back. It's multiband though.

Multiband is just one of the options. LimiterNo.6 is one of the best regardless of price IMHO.

 
If you're patient (and you have the ProChannel in your version of X2) you can wait for the Concrete Limiter to go on sale for 20$.  It does so every once in a great while.

All he wants to do is prevent clipping, not volume maximization, so why not just use the Sonitus multiband? It's free, it's available, it's QCed with Sonar, and it works. I wouldn't hit it with transients much over +6 to +8 dB, but then again, I wouldn't hit any maximizer so hard it would have to apply more than 6-7 dB of maximization.

I don't consider L1 to be all that transparent by the way, maybe W1 is more so? I think L2 is the "transparent version".

And thanks for the Limiter no. 6 heads up. I really need to try that out sometime.

Thumbs up on the Concrete Limiter! Once I got that plug it virtually replaced Ozone with the plugs available in Sonar.

Sanderxpander
I don't consider L1 to be all that transparent by the way, maybe W1 is more so? I think L2 is the "transparent version".

And thanks for the Limiter no. 6 heads up. I really need to try that out sometime.

L1 is nowhere near as transparent as L2, but for the mild use  the OP seems to need,I believe it is up to the task.  The differences really come into play when you try to maximize. Doesn't sound like he plans to push it at all.  I like Limiter no 6 but I think the interface is clunkier than W1 for simple needs and at that level does not sound noticably better. It's all preference of course but.  I weill add the discliamier that I have used W1 for audio limiting in video projects more than audio.  At the time I started using it, I needed a free limiter that actually worked in my video editor and it fit the bill.  So we are not talking about taming clipped audio or major attempts at leveling.  For the most part I was just making sure audio already at decent levels were limited to -6 or -12.

Thanks to all for your suggestions.  Very helpful indeed.
 
So it looks like I have some homework to do - so far I've been checking out the sonnitus multiband and the LoudMax plug-ins.  Both seem fine for what I want to do.

I used to always use either Waves or Sonnox limiters. Always. Then I got the Concrete Limiter and that's it for me now. I love the Concrete Limiter. It just sounds perfect for my style.
PS
For a freebie, the Vlad G Limiter 06 is amazing, too.

I've been using Boost 11 for years now. Granted, it's not free if you didn't buy a version of Sonar with it bundled, but I've tried several other limiters and always end up coming back to Boost11.