As you can see there are many options available and many advocates for each. I'll throw in my two cents ...
Skip iPhoto entirely. It really doesn't help anyone learn how to handle either jpeg or RAW files in a way that is fully understandable. I say this because it was meant to be easy and in that, a bit too easy taking real control out of the end users hands and placed in "controls" that are over generalized.
For typical organizing and "adjustments" good options remain with Aperture and Lightroom. For advance alterations of images, you can look into options like Pixelmator or climb into the Adobe Photoshop camp.
The nice thing about Lightroom and Aperture is not only do they start you with more logical and practical understanding of how to handle your image files but they take 3rd party plug ins that add extra options to what you can do with your images. Companies such as NIK and OnOne provide superb plug ins (and they also work with Photoshop).
In my situation - I work with scanned images and thus Photoshop is my tool of choice for this type of work (restoration and retouch).
For photography, due to the type of RAW files I have, I find that Capture One is a better fit (Fuji RAF files don't do as well with the typical post processing/management software).
I have worked with Lightroom, Aperture, and DXO. I think anyone starting out would be wise to get one, stick to it for at least 6 months before sampling another. They all provide good understanding of what can be done and how to manage - catalogue. I added DXO as it too has some excellent tools though the first two have the ability for the plug ins. There is no need to get Photoshop to start with but if you think you might want to experiment then go with Pixelmator. (Unless things have changed, Adobe PS Elements does not provide end product files in 16bit but rather 8bit.)
Most of all - enjoy learning and experimenting.
