Recommendations for a very good lock?

The biggest things to consider are how expensive the bike is, how obvious that expense is, where you will park it, and how long for.

The best ones tend to be thick shielded cable types or U-locks which will discourage opportunists (key lock, not coded). But, if you leave the bike all day in a quiet area, then it doesn't matter what sort of lock you get. A decent thief has plenty of time to break it. Increasingly, bike thieves know what they're looking at and are prepared to work on a lock for a bit if they know the bike is worth it.

Consequently I would never ride my pride and joy to work unless I could bring it into the office with me.

Busier parking areas offer less opportunity, but if you act confident (and don't look shifty) then passers-by will let you do pretty much anything.
I park my commuter in an area which has suffered thefts in the past (despite high pedestrian traffic). My saving grace is that there is always a few others who have not bothered to use a lock or have only used a flimsy one (making their bike easier meat than mine).

The best lock is to not leave the bike out in dodgy areas for extended periods of time.
What exactly 'extended' means will, of course, depend on the area......
Pretty much any lock should, prevent casual thievery if you're just stopping into the store for 10 minutes.
(Although it will not prevent theft of your handlebar bag, for example)
Pretty much any U-lock will prevent theft by anyone other than a pro with a reciprocating saw.
If you live in an area where such elements roam the streets during daylight hours (or you are forced to leave the bike outside overnight), the best bike lock would be to move elsewhere.
Yeah, I know - easier said than done.
If your neighborhood is indeed a war zone of sorts, sometimes the best theft prevention is to make your bike look as crappy as possible.

Tafi, Nukuhiva,

Thank you very much for your posts. I've been to a couple of shops today to have a little look and I'm quite shocked at the weight of some of them!! 🙂 especially the kryptonite new york (recommended by a friend today). Carrying that around should certainly help lose an extra few pounds 🙂

My first form of protection will be the £4 per month insurance quote and then make a decision on a lock 🙂

Nukuhiva, that's the ultimate plan, to get away from Liverpool, preferably San Franciso. Possibly the greatest city to cycle in 🙂

Thanks very much guys for your help and advice, it's greatly appreciated 🙂

Quoted post said:

Originally Posted by Nukuhiva [IMG]/img/forum/go_quote.gif[/IMG]

Pretty much any U-lock will prevent theft by anyone other than a pro with a reciprocating saw.

Not necessarily. The fastest method is to use a car jack to break them open. That said the u-lock is still the best type for security. The question is whether you want to lug one around.

Thanks Tafi 🙂 apologies for late reply, no Internet connection 🙁 Looks like it's the NYC bad boy as it is on the 'required' list for my cycle insurance. Big ass backpac to house a big ass bike lock is next on the shopping list 🙂

The best lock is to buy a cheap used bike for around $50 to $100 American dollars and ride that where ever you need to lock it up! I'm serious. Any lock can be defeated...ANY LOCK. Simply get a cheap lock and lock up your cheap used bike, expensive locks can cost $200 and still be defeated, so why spend $200 for a lock when a simple $40 dollar lock on on a $75 bike will work just fine. Leave your good bike at home and use it when you know it's not going to be out of your sight.