How do I create a keyword list based on user input?

How do I create a keyword list based on user input?

I need to be able to have a list of all keywords that have been entered popup so people can choose from existing keywords, or add their own, the way Google blog does. How do I do this?

Is there an "other" feature in the value checkbox lists that people could put in their own words for categories etc.?

I have to fix this to finish off our database and "go live. Help! Thanks, CatherineTodd, ctodd1000 at gmail dot com.