This is an argument that can go on forever. I typically carry two knives; one fixed and one folding. A folding knife is definitely the more socially accepted knife to pull out for everyday use (opening a letter, cutting a string off your jacket, et cetera.) However, fixed blades tend to have strength and ergonomics that can't be matched by folders. They have blades of all different shapes and sizes, handles with many different materials, and all kinds of nifty things built in. As I said, I carry both. My folder is a Columbia River Eros
(Don't worry, they can be had for half the price) and my fixed blade is ever changing dependent on my dress and the situation.
Columbia River makes some excellent knives at pretty good prices. They might not be the extreme durability of Extrema Ratio, but they aren't the prices of them either. As for CRKT fixed blades, I suggest checking out their A.B.C., Crawford, or Ryan Plan B for smaller fixed blades at great prices. For something huge, check out the Ultima; it's the most comfortable knife I've ever held. Ever.
Of course, SOG makes some amazing pieces, as does Cold Steel (I love The Spike), Extrema Ratio, Buck, Ranger, Parker, Ka Bar, and all the other names you already know. Another advantage to venturing into fixed blades are all the independent, professional knife makers out there willing to make you something custom. Ben Tendick's BPK (Bomb Proof Knife) is absolutely gorgeous worth a look.
Essentially, as with many things out there, it comes down to preference. I definitely prefer a fixed blade, but I tend to get some good stares at work when using one to open my pay stub. So, I do exactly what you're contemplating: I carry a folder for mundane tasks, and a fixed for heavy-use/self-defense. They are fast into action, no stupid safeties or levers to mess with during high-stress situations, and the hinge will never break.