WFRP may be a good buy. It's low-magic gritty fantasy, and not a d20 System game. If you prefer d20, then I guess you may want to avoid this.
Mutants & Masterminds 2nd Edition may also be good, along with the book for GMs I think that came out a little while after it (can't remember the name; but from what I read it seemed like it was a useful resource for the game). That's a superhero RPG that's roughly based on the d20 System, but rather different in many ways. Again, if you prefer d20, you may want to avoid this, but M&M is at least moderately based on d20, just broken down into a point-buy system for superhero campaigns with a lot of changes.
If you have D20 Modern and D20 Future, and like the old Transformers cartoon or comic books, then Mechamorphosis would be cool. It's in the Horizons line of products, but I can't quite recall the name of the company that publishes it.....FFG? Green Ronin? (curse my poor memory! .....and I really need to get this book, dangit, I just haven't had any spare cash....) I don't recall if it's PDF-only or an actual in-print book (I think it's a print book).
Similarly, if you like D20 Modern and/or D20 Future, you could look into buying Grim Tales or the Blood & X series; GT is a modified or dissected version of D20 Modern, sort of; Blood & X is just a series of 3rd-party books or PDFs by Chuck Rice (EN World poster 'Vigilance'), and highly praised. There's Blood & Fists (martial arts book for D20 Modern), Blood & Space (not hard to guess what this is), Blood & Circuits (cybernetics IIRC), and others, including one or two sequels to those (I don't remember which ones got sequels). I think Vigilance also made (or maybe is still finishing work on?) a game called Legends of Excalibur, for the historical or fantasy genre based in Arthurian legend (I can't recall exactly, and I think it's d20?).
If you like or don't mind Monte Cook's work, then the book Monte Cook's Arcana Evolved may be a good alternative to D&D for you. It's the updated and expanded version of Arcana Unearthed, and Lands of the Diamond Throne, combined (IIRC). Different races and classes from D&D ('cept humans are still around in it of course). I think some of the other supplements or adventures for AE would also be good investments.
Iron Heroes is a good sword & sorcery RPG using the D20 System, and you can use some D&D material alongside it without much difficulty I think. Iron Heroes is probably what Conan d20 should have been; but note that it can be tough to grasp at first, especially since the whole group has to grok it if they're going to use the combat changes effectively. It's extremely low on the 'sorcery' side (the Arcanist class in it was literally thrown in as an afterthought, for those who wanted some evil sorcerers or whatnot, but it's not so good for PC casters), and the rest of the classes in it are made to fight awesomely without relying on magic items or large wealth.
Since they're made like that, you don't really have to use magic items in the game and you can generally restrict them to the rare discovered artifact or minor items that're more flavorful/utilitarian than actually useful. There's now a supplement, I think it's called Mastering Iron Heroes, which really helps out and provides some villain classes for the GM to use (I don't recall if it includes any different rules for sorcery). And the Iron Heroes message boards have several variants or replacements for the Arcanist for those who want to salvage that class. Iron Heroes was published by Monte Cook's company, Malhavoc Press, and the print versions were put out by Sword & Sorcery Studios (same as with all printed Malhavoc products I think). However, Monte did not get involved in IH, it's Mike Mearls' baby.
If you like the cyberpunk genre or whatnot, or just the idea of near-future dystopia with cybernetics and all kinds of guns and stuff, you might like Shadowrun. Shadowrun blends cyberpunk with fantasy, basically. Right now SR 4th Edition is out, but 3rd Edition is still available, and that's what I've played (and prefer; 4E changed a lot when it updated the timeline). The Awakening returns magic to Earth catastrophically in the near future, various states and nations are devastated by the natural disasters and other problems, and then megacorporations start to become the real political powers in the world.
Orks and trolls struggle in the slums to protect each other and get fair treatment as part of the Ork Underground, dwarfs and elfs enjoy a relative sort of normalcy while making a living as movie stars or techies or whatever, the elves of Tir Na Nog and Tir Tairngire bicker and politick and try to spread ideas of elf supremacy, the Humanis Policlub lashes out against nonhumans, street magicians and street shamans work their sorcery and duke it out with hostile spirits or paranimals (paranormal animals) for profit, dragons prowl about their territories or dominate megacorporations with their wealth/power/magic/intellect, the Native American Nations squabble and work to maintain the freedom of their reclaimed lands, street samurai run around with obscene amounts of cyberware and firearms, deckers/hackers have their fun on the Matrix that replaced the internet after a terrible virus years ago, corps and governments have turf wars and all kinds of black ops going on in the shadows, and shadowrunners sell their skills like mercenaries either to make a living or occasionally to rail against The Man or corruption through sabotage and theft. Etc.
Figure out what kind of system or genre of game you want to play, and make your decision from there, naturally.
