Okay, okay, technically this program is not a web tool. Sorry about that. But you download it for free off the net, so that's gotta count for something.
Audacity is the other item on my top 12 list that requires a download and install. Google Earth (# 8, see below) was the first. It is open source, free, and relatively light-weight. There are many other audio editing programs out there, but this is my choice. Years ago I started using Goldwave which is a very good editor. Goldwave is shareware, so I prefer Audacity since it is FOSS (free and open source software), or FLOSS, as some are trying to call it.
From the Audacity Book by Matt Brubeck:
“What is Audacity? Audacity is a free software program for recording and editing audio. Audacity runs on several operating systems, including GNU/Linux, Mac OS X, and Windows."
"You can use Audacity to record sounds onto your computer, either live (with a microphone) or pre-recorded (from tapes or records). Audacity can also open and edit audio files, including tracks downloaded from the internet or copied from CDs. Audacity can open and save Ogg Vorbis, MP3, WAV, AIFF, and several other types of audio files."
"You can edit recordings with Audacity the same way you edit text with a word processor. Audacity can cut, copy, splice, and mix sounds together. Filters are included for altering speed and pitch, adding echo or reverb, removing noise from recordings, and more.”
- Wesley Fryer has a quick-start guide and several other useful links on his podcasting wiki .
- djweinstein has created a Flickr show about how to use the Time Shift tool in Audacity. Time shift is an important tool for editing video.
- Dan Eliot has developed a step-by-step tutorial for using Audacity.
- Audacity developers have better than expected documentation and help available at thier own site as well.