searched around "Googled around" for a nice jQuery Tag editor, and it took me going through quite a few plugins before I found one that had everything I wanted... which included Autocomplete functionality using jQuery UI core. It looks nice, uses built-in Autocomplete, and has all the tag editor features. I must note that it works a little different then almost all other tag editor plugins I've seen in terms of work flow. It considers "remove from list" and "delete from list" two separate functions (read this). This can be very useful, or merely extra work, depending on your implementation on the back-end. Currently it is being actively developed by Oliver Albrecht (aka @webworka) and hopefully it stays in active development!
I'm using it in the revamp for the CouponFollow website which I hope to push into private beta before the end of the month, and roll live shortly after. I'll likely use this plugin in future projects as well.
Here are some others that I liked but didn't make the final cut for this project.
*jQuery Tag It!
My Notes: Very simple, autocomplete using jQuery UI. Tagedit is based on this one.
*jQuery Tag Editor
My Notes: Good but no autoComplete. Some CSS overflow issues with large amount of tags.
*jQuery Tag Suggestion *
My Notes: Good, simple. Slick auto-complete, but no spacing support. Older, not actively developed?