[ValhallaGH]

Paragons is good. Lots of example characters, some really neat ideas. But it's weak on organizations, super-tech, and some of the example builds don't make any damn sense (Why is Blue Shift is a master of defensive combat, instead of Dodge Focused? Why does Nightstalker need to be able to harm Impervious 12 characters?). If you can only pick up two books, Freedom City is probably a more useful setting to swipe from (though some of it's builds are just as screwy - Arggo and Meta-Grue come to mind, along with Lady Liberty's Healing 11), and Instant Super Heroes is almost exactly the sort of thing the OP is after.

True 20: I love Blood Throne, so I'm biased towards it (I even have a small development credit). That said, I think it's got some really neat mechanics in there, and showcases the flexibility of the True 20 system quite well. The blighted bestiary and blight elves supplements are great, especially the blight elves book. Lots of really nasty ideas (RP, plot, backstory, and mechanics) along with enough mechanics to make it well worth the price. Also, Reality Deviant Publications is a great publisher to deal with.
Reign of Discordia is an amazing setting with great support for Sci-fi, especially for space craft and cash rules. Another RDP products.
I'm unfamiliar with Interface Zero, since I don't own it, but what I've seen is impressive. If I was at all interested in cyper-punk then I'd snap this up and drool all over it. Once again, RDP greatness.
Nevermore is fun, and Dream conviction is cool, but it's not quite my cup of tea. Still a great book.
Caliphate Nights is beloved by many, but it's not my thing and the publisher has stopped supporting it; still a lot of neat ideas and some mechanics that still get mined by most posters on the True 20 forums.
Technothrillers is pretty good. A solid supplement for super-spies but only so-so for other modern genres. A lot of mixed reactions to the initial release, but RDP is good about updating and improving their existing products (and providing free updates to customers).
Darwin's World is Darwin's World. Not a lot that's new but a lot that's fun, and Vigilance always makes you rethink stuff.
Wild West is simple and solid. Not much new, and there didn't need to be. Good flavor, low on mechanics.
Legends of Excalibur is great but again, not a lot of new material. Little that you couldn't already do.
If you just intend to mine for generic characters and adventures, then probably Blood Throne and Interface Zero will be your best purchases, giving you a really wide variety of supplemental mechanics. But as you can see, it's difficult to narrow it down to just those two, and I'm continually tempted to suggest other works as well.