Lick Lick,

It should be a "boing" like spring. If it's an older guy, it should be the sound of a creaking door opening slowly.

Exactly what I was gonna say...that or an elevator chime with the voice that says "Going Up"...works for "Going Down" too

I'll go with the creaking door opening and closing sounds for rising and falling erection.

on the way down, the theme from "Monty Python", or "Look on the Bright Side of Life" .

The sound of the crack of the bat and the roar of the crowd as the baseball leaves the field.

here it is ! erection sound

see archer link  

... "How you doin'?" (in the voice of Joey Tribbiani) :P

Schwing!!