Possible Namecoin use cases
Domain names - can be shortcuts to regular domains
Personal Namespace
Messaging System
Alias system / Identity System in bitcoin, alt-coins, bitmessage, etc
Login system (See http://p2pconnects.us/2013/05/10/namecoin-cryptographic-login-that-doesnt-suck/ for example)
Notary/Timestamp system (See http://news.techworld.com/security/3449015/could-the-bitcoin-network-be-used-as-an-ultrasecure-notary-service/)
Web of trust (like http://bitcoin-otc.com/trust.php and more)
Unified Bitcoin Payment Address System
Bonds
Shares
Voting
Torrent tracker via magnet links (See discussion in the bitcointalk forum)
Public file signatures https://bitcointalk.org/index.php?topic=210876|bitcointalk