It’s a rainy day and I’m bored not to mention sick of reading a bazillion threads asking about bike security so hopefully this will answer all your questions. I’ve done my best to cover everything but feel free to post up if you have anything to add.
1. Physical Devices
Several different locks are available and each has it's pros and cons. Go to your local bike shops for more brand specific features but here's a general overview.
Disc Lock: Nice and compact and very popular. It’ll fit in your trunk and is highly portable. This lock will mostly likely deter the quick grab and go thief but won't to much to protect you against the guy with a pick up truck. Some manufacturers offer a built in audible alarm but I really don't think this will do much for you when it's in the back of a truck driving off in sub 30 seconds. NOTE: Kicking your bike after you attempt cruise outta Starbucks only to realize you forgot to remove said disc lock will not stop the chicks from laughing at you. See http://www.kryptonitelock.com/inetis...s_item&pgrp=20 for example.
BFC (Big F'ing Chain): Slightly more useful then above listed disc lock albeit slightly more cumbersome. Transport is always an issue with these. They weight a TON and make a heck of a racket in your trunk. It is not acceptable to wear it around your neck and no it won't make you look like 'one of those dudes in the rap videos'. If you have something large and immobile near your bikes parking spot these security devices are one of the better theft deterrents. NOTE: Make sure you get a good lock such as a mini u-type lock as most padlocks will probably be too easy to pick/break. See http://www.kryptonitelock.com/inetis...s_item&pgrp=20 for example.
Brace: These are probably the most effective theft deterrent available for your bikes parking spot. They are a heavy duty steel fixture that you fasten to the concrete floor of your garage/drive way that has a bar that goes through the wheel of the bike. Obviously they are impossible to transport and therefore will only be of use at your home. One manufacturer makes these locally in Vancouver and more info can be found at http://www.bikebrace.com.
2. Electronic Devices
Every man loves gadgets and there are several different ones available to protect your bike. Again manufacturer specific features may vary so do your research before you buy.
Alarm: Find a motorcycle specific alarm as they tend to be a little more compact and have features that are particularly important to bike owners. One such feature is a proximity sensor. This sensor can usually be adjusted to sense when someone comes within 'X' number for feet/inches from your bike and give a warning chirp to let people know it's protected. For those of you who are tough guys, an alarm with 2 way communications will notify you when your alarm has been tripped so you can promptly lace up your steel toed boots and rush outside to beat the 'philthy MoFo' who is attempting to pilfer you pride and joy. Again, a local BCSB member manufactures some great motorcycle specific alarms and more info can be found at http://www.talonalarms.com/.
GPS Tracking: Not overly useful in preventing theft but definitely the cats ass as far as post theft vehicular recovery is concerned. These units work with satellites to keep track of your bike and help police or your bad azz cousin locate your ride and maybe even the perp(s). I believe there’s a monthly monitoring fee with these devices but again see the individual providers for specifics. http://www.talonalarms.com/ also sells these. NOTE: When not being used on your bike these devices can also be useful in keeping tabs on cheating girlfriends/wives (I'd leave it on the bike, you can always find another woman).
3. Environmental Devices
Location, Location, Location: Choose where you park your bike with thieves in mind. This is one instance where 'out of sight, out of mind' isn't always the best motto. Well lit, high traffic areas are often better then secluded dark parking lots because the thief will have to be quicker and may possibly get spotted. In quiet secluded area they'll have all the time they need to get your bike and will see you coming a mile away. Other ideas are parking your bike INFRONT of your car in underground lots (pinned between the car and the wall) or even somewhere you can check on it easily from a window or security camera.
Out of sight, out of mind: Yeah, I know, I'm contradicting myself but this does apply to a certain extent. Common sense (which, unfortunately, isn't so common anymore) dictates that if you have an enclosed garage in your home you'd be using it for your motorcycle. Unfortunately if your garage is already filled with your 2006 Porsche Carrera GT and 2005 Ferrari Enzo then I have no sympathy for you and wish that you die in a fire you rich bastard. Anyway, covers are also a good way to keep prying eyes away from your baby and protect it from the elements at the same time.
Rottweilers & Rifles: I don't expect you to purchase a dog or a gun but if you already have either of these here is yet another use for them. The canine part more specifically, as even an ill-tempered Chihuahua will usually do a pretty good job of alerting you to suspicious figures lurking in your yard and possible even frighten them off. As for the firearm... that's your prerogative and I take no responsibility for your actions.
All this being said, it's same as that lesson you learned the first time your girlfriend was a few days late: There's not such thing as too much protection! The best advice I can offer is to use as many of the above described techniques as practically possible and invest in good quality theft deterrent devices. Never forget to use your built in security devices like your steering lock and removing your key from your ignition (duh, right?).