Re: A good low fantasy game
If you can get your hands on the Valdorian Age, I highly recommend it. It's sort of like plopping Fritz Leiber's Lankhmar down into Howard's Hyborian world, and adding the magic of Moorcock's Melnibone. The book is worth its price for the magic system alone.
If you can't get it for whatever reason, in building your own low fantasy world, a lot of little countries makes things interesting, especially if you're able to work in a bunch of exotic cultural tidbits. There is a lot of Conan material scattered around the Internet...file the serial numbers off of some of that stuff for a good start.
Magic should be slow and unwieldy...Extra Time, Gestures, Incantations, Concentration are good Limitations to use as a baseline. It should also carry other drawbacks...magic in the Valdorian Age uses the concept of Favors, where sorcerers in essence get supernatural forces to do things for them in exchange for doing something for the supernatural force in return.
One system I used a while back broke magic into white and black. White magic didn't carry any additional drawbacks, but it wasn't useful for combat. Black magic was good for combat, but using it too much could warp the mind, body, and soul (Side Effect that Transformed the caster, adding Physical Limitations, Psychological Limitations, Berserks, Vulnerabilities, Susceptibilities, etc). "Gray" wizards used black magic, but only for minor things...below a certain threshold, they didn't have to deal with the warping properties of the magic.
As far as plots and stuff, that's pretty general info that isn't really specific to low fantasy. You should be able to find a lot of that here and there on the Internet. Robin's Laws of Good Gamemastering might be useful for you, and it's pretty cheap.