Altium has made a big splash with its free CircuitMaker software, so we’ve added it to our list of free CAD software (although, as of this writing, it’s in “public beta”; it hasn’t been released yet).
CircuitMaker imposes no limits on the complexity of the design – the one gotcha is that your projects are stored publicly, online, and “[b]y using CircuitMaker you acknowledge that any project you post will be subject to one or more open source software or hardware licenses. The exact terms of GPL, LGPL, and some other licenses are provided to you with your particular product.” That doesn’t mean you can’t use it on commercial products; it just means your board design will be public.
It also means that you must have Internet access to work with your design.