I've been looking for a way to generate any Unicode character on an iPhone or iPod Touch but have not found an app yet which does this. I tried a variety of charts and virtual keyboards reachable via Safari, and the best one seems to be
Macchiato's Character Picker
You can adjust the page size and save it to one of the app screens, and then select the character range that appears on the virtual keys and input them into the text box at the top. Unfortunately the device keyboard pops up after every entry, but you can dismiss that. In order to copy/paste the result you have created, you must let the Apple keyboard remain after inputting your last character.
(12/15) The iPhone/iPod Touch app Unicode Table now has a copy/paste function for individual characters which is easier than using the website mentioned above.