For DTP only, the best is probably Swift Publisher. I got it as part of a bundle a couple of years ago.Swift Publisher now has support for Art Text, another BeLlight program. I do like Belight Software programs.
I use Pages, part of iWork, but it does lack some features a dedicated DTP program would have.
Another, not as highly regarded any more is Desktop Publisher Pro. It is PPC only, not universal binary.
In my opinion iStudio Publisher is the best and easiest to use dtp application for the mac. I found it when I switched from the PC and haven't looked back!
Having previously used it on Amiga and PC, my preference is Pagestream. It's got plenty of features, but admittedly is not the most user friendly and is still suffering with some OS-X compatibility, although the latest beta is looking better.
If you have Word, take a look at the publishing mode. It doesn't have all the features of a proper publishing app, but if you already have Word then it might be good enough for what you need.