iTunes link: Vlingo
Vlingo enables you to speak into your iPhone and have what you say transcribed into text. You can use it to search the web using a variety of search engines such as Google and Bing, but also perform a range of other functions including dialling a contact, searching for a location on a map or updating your status on Facebook.
You can also make in-app purchases to add additional features such as the ability to use your voice to email friends or send text messages to your contacts, although the later merely translates your speech to text and then makes you cut and paste the results into a new text messages, which is hardly ideal. Once Vlingo has translated your speech into text it offers a preview of it so you can edit it to correct any mistakes.
Verdict: The extra paid for features are perhaps a tad overpriced, but Vlingo still offers enough features for free to make it well worth a download.