There are a lot of apps that allow you to do simple voice recordings in the App Store, ranging in price from free (EverNote -- includes this capability)on up. However, perhaps because of its generic name, "Recorder" from Retronyms, is the leader in the space, with a ranking of 15 of all paid apps on the App Store (iLounge has a good roundup of other apps in the recorder space).
As one review said on iTunes: "This is the best dollar we ever spent". AppCraver is likely to agree. This well-focused app does one thing and does it well: record messages. With a big record button, its not hard to see how to record a new message. When done, click on the blue button to change the message title (and other attributes) and then email the message to yourself or your friends.
In any case, the app is great and totally justifies the $0.99 price tag. Great work.