Quick release skewers make life easy - except when you have to leave your bike parked up.
Ditch the extra U-locks and insecure cables and use Pinhead Components' handy lightweight locking system for your wheels, seatpost and fork. The skewers replace normal QRs and are easy to install. The important thing is to remember to bring the key when you ride in case you get a puncture - the same key, with handy bottle opener, fits all the locks in the pack.
The fork lock adds some extra protection in dodgy bike parks and
the top cap looks cool too. But be aware that some seat clamps aren't compatible with the seat lock, because it can only be fitted in place of standard seat clamp bolts.
Overall, the Pinhead locking system is best for your city ride, and it's also great for your mountain bike if you have to leave it alone for a while.