Spice analysis:

I find Spice Analysis quite useful, although not the last word in aiding circuit design.

A copy of the excellent "Tina" software is avaible for download from TI's website.

Click here to go to the download page.

Schematic Capture / PCB Design:

Previously I used DOS versions of Orcad (schematic capture) and Tango (PCB Design) - it is possible to export a netlist from Orcad, and create a "rats nest" for PCB layout in Tango.

These two programs can be found on the net if you search for them (hint p2p).

Orcad used to do a free (I think) version of their Schematic Capture software called Orcad Express - I think this was intended for use by educational establishments.

Loudspeaker Design: