How much light is "bright enough to light a room for reading"? That can vary a LOT from person to person. Personally I prefer at least 3000-6000 Lumens in an average sized bedroom to read comfortably. I can get by with the 18L setting on my zebralight though... camping and stuff where I am not reading for long periods.
+1 for the Rayovac Sportsman Xtreme lantern. For $25, u can't beat it. Its compact, its tough (i've dropped mine many times), and it only uses 3 D batteries. Plus it gives off a good amount of light, but like was mentioned, it doesn't have a very low low. In fact i usually just leave mine on in low mode because its really not too much dimmer than high.
If you want something compact with a real low, check out the black diamond lanterns. They have the ability to ramp up and down in brightness.