To assure that, you want to either keep your bike somewhere where you can keep an eye on it at all times, such as next to your desk (which my work does not allow), or securely lock it to something immovable. But, locking it to something secure isn't always going to guarantee your bike will be rideable when you leave the office...
I'm sure the only reason there are still crank, pedals, and a seatpost is the theives did not have a crank puller or the right size of hex wrench with them.
To make sure your bike remains intact, you could use multiple locks and chains...
Or, you could invest in a system that secures the individual components on your bicycle. Pinhead Locks is one such system.
I met with the folks from Pinhead Locks at Interbike, and they sent me their Total Bike Protection package, as well as a saddle lock for review. The Total Bike Protection package comes with front and rear locking skewers, headset lock, seatpost collar lock, their frame lock, and two keys.
Unlike some other locks, the Pinhead system replaces your skewers, headset bolt, seatpost collar, etc... with their uniquely keyed bolts. The design of the bolt heads make it extremely difficult to remove except with the correct key.
Installing the new locks is as easy as performing any regular maintenance on your bike (be sure to note your saddle height). Replace your existing hardware with the Pinhead locks, tighten them down with the key, and you're good to go!
Wheel skewer locks.
Seatpost clamp lock.
This carbon post is the only one I have that has a single, downward-facing bolt - which is needed for the saddle lock to be effective, as it restricts access to the hex bolt.
The shackle shape on their gold-rated bubble frame lock is designed to be more resistant to jacks and crowbars. It is made from hardended steel and has a double bolted shackle. It also has a hidden key entry for additional security.
And an added bonus, the key works as a bottle opener!
I haven't tested out the effectiveness of the locks as I don't feel like putting my bike up as "bait", but I won't be as paraniod with leaving my bike out of sight when I'm downtown with my bike now.
The only suggestion I would have is if Pinhead could include a mounting bracket for their frame lock. I found the bag it came with bulky, and as for now, the lock resides in my backpack when it isn't securing the bike - which means I have to bring my bag, or use another lock for quick trips.
The Pinhead locks start at $39.99 for the seatpost or saddle lock, and go up to $149.99 for the Total Bike Protection package. Check out www.pinheadlocks.com for additional information.