The LM386 amplifier and a parallel port controlled relay switch
The LM386 universal audio amp is really handy for boosting audio before feeding the transmitter. Low power AM transmitters love to get hot audio, the more the better. Giving plenty of oomph in the audio will give the modulation section plenty of signal voltage to work with and that will better modulate your carrier wave.
Some low power broadcasters who are disappointed with their range are simply under-driving the modulation section. Drop an LM386 booster amp in your audio chain and see what happens!
There are many ways to get your hands on an LM386 booster amplifier. You can pick up a chip and build your own from scratch, using LM386 Booster Amplifier plans like these. You can order an easy-to assemble-kit from an electronics vendor. Either way, it's an uber simple solution!
A parallel port controlled relay switch can be the centerpiece of a simple station automation system. The relay can switch various audio sources and provide an easy way to bring NOAA Weather Radio, local TIS stations, police scanners and other odd ball audio sources into your station playlist.
Connected to any old PC, managed using anything from home automation software to a DOS batch file, the parallel port relay can easily manage all of the connections you can throw at it. Just like the LM386 Booster Amplifier, you can build a simple relay from your junk box using parallel port interfacing plans, or you can order a nice, eight-relay kit.
Put it all together, it spells lots of fun for almost free :-)