An accurate tuner is an essential tool for live performance and studio work, but especially so for doing guitar setups. The new Peterson StroboPlus HD is accurate to 1000th of a semitone and features aback-illuminated LCD.
Mic stands are an essential bit of gear that few people spend enough time thinking about. Really well–engineered stands are frustratingly rare, though.
I discovered this very handy software, created by the makers of AA Translator almost by accident after searching for a way of batch–interleaving pairs of mono WAV files.