Adobe Elements (when I used it on Windows before migrating to Mac) is pretty good. It's Organiser is pretty useful, can handle RAW (but not batch processing), you get a baby-version of Photoshop for further editing.
However, if start building up big collections of RAW files, Lightroom (or Aperture) is going to be a better tool for that.
As you have discussed, it sounds like you need some extra pixel editing as well. For now, I use GIMP on my Mac. Basically, use Lightroom to get balance, colour corrections etc etc done. Then any extra effects if required in GIMP.
However, having got used to Photoshop Elements on my old PC, I would like to use that again. So what I suspect I would do is get Elements 5 when it comes out for Mac (this should be a Universal Binary for Intel Macs).
Thinking about it though, you are wanting to add borders to your images, right? Why? Are you adding borders to make the images look better when you include them in a online gallery? Don't forget, you can build a online gallery using Lightroom (HTML or Flash). Also, other online Gallery software can also automatically add borders to images (I'm thinking of Menalto Gallery 2 for example).
Also, did you want to add borders to images for when you print them out? Again, from Lightroom, the Print module allows you to define that.
So, it may be that you don't actually need to alter the image and add a border at all in the first place. Depends really on why you wanted the borders.