I figure I'd take this opportunity to shamelessly plug AudioX, which lets you search and play 21,000+ sound samples built into World of Warcraft.
How does this help with addon development?
Well, AudioX can be useful in locating samples that you wish to replace, silence (via the data folder e.g. Silent Horses, Silent Squire etc) or utilise in your own addons. Think of it a bit like TexBrowser but for sound samples instead of textures.
AudioX also facilitates linking of sound samples via chat hyperlinks, but that's outside of the dev tool remit, so shhhh