Recommendations for multiple HTML / Ajax selection using autocomplete library or plugin

Question

I am looking for a library or jQuery plugin (etc.) for a dynamic multi-valued form selector. Think of the gmail "TO" field when creating email.

Are looking for:

• Fill in the field with employee identifiers from 0 to n.
• There are currently 5,000 employees.
• Search for a first or last name.

I rolled my own in the past. However, I try to focus my development time on specific business issues.

Thanks.