See if your computer has a microphone built-in. Just open Sound Recorder (or Sound Studio if that's still being included with Mac OS X, I doubt it though), set it to record, talk at your monitor, and see if anything comes up. Then just save as .WAV (preferably .MP3 if it's long) and upload it somewhere. Maybe one of those drop-file websites.
I could have sworn I've been able to record without a microphone before just by yelling at my speakers, but then, I also had to change the speaker cable to Line In or something, and with nothing going into Audio, I couldn't record and hear myself at the same time. Not sure if that worked.
There's also handheld recorders you can pick up that have USB so you can put your recordings onto your computer.