Electronic CAD programs for the DIY'er
CAD programs for the DIY'er can be prohibitively expensive. But at some point if you want to do a PCB design or even a decent schematic, it's a necessity.
I've had good luck with two programs that can be had in freeware versions (of limited size) and in reasonably priced "full" versions...
PADS-LOGIC and PADS-PCB
PADS software (or whoever owns it this week... EDA vendors get bought and sold so fast I cant keep track of them) has been a major player in PCB design for many years. Their current PCB package runs around $20,000 for a full license.
Luckily, there is a limited version of the old (circa 1989) DOS-based PADS-PCB which can be downloaded for free. It is limited to boards of less than something like 100 components, but can handle a lot of the things that a DIY audio guy wants to do. The accompanying schematic package is called PADS-LOGIC, and it is also available for download. It's not my favorite schematic program (OrCad is too deeply embedded in my brain) but the price is right - a full OrCad license is around $7,000!
You can download PADS from this site: http://eeshop.unl.edu/cad.html. There are also other programs and links to be found here.
Eagle CAD
Another popular CAD program that is available in a limited version free is Eagle CAD. The free version can only lay out small PCB's (like 3" x 4") but otherwise is fully functional.
The nice thing about Eagle is that you can get a full, unlimited version for $800. That might sound like a lot for a hobbyist.. but hey, I know guys that spend thousands of dollars on mountain bikes, or even on audio interconnect cables! (don't get me started...) It's a whole lot cheaper than OrCad or PADS, not to mention the big-ticket EDA tools.
I've used several of the >$20,000 CAD tools (in my "day" job), and although Eagle doesn't quite do everything they do, it's pretty darned impressive for the price. You really can do professional designs with this product.
You can look at Eagle and download the freeware version at www.cadsoftusa.com.
UPDATED 7/3/07 - You can download my Eagle library. As-is, use at your own risk! wheat.lbr, 75kB (zipped)