SoundCloud is an online service for recording, hosting, and sharing audio tracks. You can use SoundCloud to upload and share audio recordings that you have stored on your computer. SoundCloud can also be used for directly recording a spoken track. One of the really neat features of SoundCloud is the option to comment on tracks as they are playing. To make a comment just play the track, click on it, then type your comment in the comment box. Your comment(s) will be attached to the spot in the track that you clicked on while listening. SoundCloud has apps for Android and iOS devices.
Audio Memos is an iOS app for creating and sharing audio messages. The app is available in three versions. The free version is limited to 3MB recordings, the $0.99 version is limited to 15MB recordings, and the "pro" $9.99 version has a nice selection of audio editing tools built-in. Some of the features that are available in all three versions of the app are automatic pause if a call comes in while you're recording, recording volume controls, and recording even when your iPhone or iPad goes to sleep.
Audioboo is a free tool for creating audio messages to share on the web. Using Audioboo you can record messages on your mobile device using Audioboo's free Android or iPhone apps. You can also record messages directly on the Audioboo website. Messages that you create can be shared by embedding your recording into a blog or website. You can also share messages by posting them to Twitter, Facebook, Posterous, and Tumblr.
Tape a Talk is a recording app for Android. The feature of Tape a Talk that is most appealing to me is that recordings can continue even if your phone has turned off the display (something that some other apps don't do). You can also record to an existing audio file on your phone. Recordings are saved on your phone. The free version of Tape a Talk is ad-supported while the pro version costs about $6 USD.
Hi-Q MP3 Recorder, as the name implies, records your audio as an MP3 that you can export from your phone's SD card, email to yourself, or send via Bluetooth to storage off of your phone. The app will continue to record even if your phone has changed screens or gone to black for battery preservation. The free version of this app allows you to record for up to ten minutes.