> I am working a project that needs to alert the operator of a trash truck if
> he does something "silly".  Any input on the best (i.e. cheap) way to
> generate a loud 'beep' with a PIC would be much appreciated.

There are a few options you could consider:

[1] Take a small loudspeaker (8ohm is common, though higher impedance would
    be better) and a moderate-sized cap (experiment some here); wire one side
    of the speaker to ground, and wire the other side to a port pin via the
    cap.  Loudness won't be too great, but cheap and easy.

[2] Add either a transistor amplifier or else an LM386 to the above circuit.

[3] Get a general-purpose piezo speaker; many of these can be driven direct
    by the PIC, and they can produce any desired pitch.  Their frequency
    response is terrible and their distortion characteristics are even worse,
    but for this application those shouldn't matter.

[4] Get a piezo transducer; these can be driven directly by the PIC, but they
    usually have only one pitch where they really work well.  You can drive
    them at other pitches, but they won't sound nearly as loud.

[5] Get a piezo transducer with a built-in oscillator.  These are driven by
    simply giving them power.  Simple to control, and they always run at the
    optimum resonant frequency.  Unfortunately, they are rather limitted as
    to the sounds they can produce.

[6] Use an electro-mechanical buzzer.  Some of these are cheap, but you'll
    need both a cap and a diode to protect the PIC from the electrical noise
    and spikes they can generate.

[7] Use a doorbell, before they go the way of the dodo. >:*3