OK, I admit it, on Windows I used the complicated but powerful Sony Vegas Pro, but on the Mac, I've been living with iMovie for years because it was pretty easy to use and quick to get nice looking output. But now with these fancy cameras (and greater awareness on my part...eg reading too much on the Internet), I probably need more. Also the new RX100 doesn't have an easy import into iMovie, so I need to find something that also handles color grading and post processing. As with still processing, you rapidly escalate in complexity (eg color space!), but it is often worth it.
So on the to the web. Lifehacker is usually good for these kinds of quick recommendations:

• Sony Vegas Pro. I used the original one before Sony bought it. The easiest to use on Windows (but I only have one Windows machine left!)
• iMovie. They actually list and like it
• Adoe Premiere Pro. But you have to swallow Adobe's outrageous licensing costs and subscription only model. Ugh!
• Final Cut Pro. Amazingly expensive at $1300, but lots of professionals use it. • Avid Media Composer. I hesitate to list any software that costs$2500, but here it is.

Well if you don't like these options, then there are free video editors if you dare try them from makeuseof.com:

• Blender. This is mainly a 3D modelling tool, but it can be used as a non-linear editor (NLE)
• Kdenlive. This is a Linux project, but you can build it on your Mac with macports which is basic, but on the other hand open source and is like all Linux stuff a little quirky.
• Jahshaka was previously CineFX and it does effects like Adobe After Effects
• Lightworks. This went open source in 2010 and is right now Windows only and might be easier than Blender but more powerful than iMovie
• Novacut is kickstarter funded and is another one to watch.