Considering the cost of a decent new bike, spending some cash on a reliable lock is a wise investment. Read about some lock comparisons here.

Another consideration is to keep an older bike in good working order for your trips downtown, especially for bar nights. An old bike is not a target as it has little to no resale value. This tactic has served me well for several years. Remember to remove your bike computer, saddle bags, lights, etc, when locking up your bike in a public area for extended periods.

Bike Lock Talk