A few years back on Windows Mobile, we had a nifty little freeware app called Notes2Self--the app was mappable to any key and allowed you to record a quick audio note which was then emailed to yourself for safe keeping (works great with Google tags).
Flash forward a few years and while we can't map any keys, we get the very worthy Voice2Mail app made by MaSta Software (WebIS, ironically, said they're not doing WP7--their loss). The app fetches for $1.99 with a nice free trial. The price is actually quite fair when considering how soild this v1.0 release is and how well it works.
We dig the graphics, the customization, the ease of use and options. Overall, a worthy app for those on the go or need to be organized themselves. So if you like having voice memos in your email, this is the app for you. Of course, you can also save locally, in case you don't like the email route. Check out the video and grab it here in the Marketplace.