What kind of bike lock do I need?

[SuperBunny]

I need some way of locking my new bike and also DS's to mine. Does it have to be a D lock? They're really heavy.

Where do you buy a good lock? Will Halfords suffice?

http://en.wikipedia.org/wiki/Bicycle_lock general info about bike locks not because I think you don't know what a bike lock is but for reference on some terms
It's really important to get the lock which suits your needs i.e. do you live in an area that has bike crime then you need to get a more secure lock...Sold Secure is a lock rating group and their best locks are silver and gold rated (and can be expensive, but they are well worth the money). You also want to double check with your insurance provider because some will not insure your bike unless you're using a gold rated lock. I know this from personal experience.
The easiest locks to cut are cable and chain locks, but they're only easy to cut if they're badly made. But D or U locks can be jimmied or pried or cut too as I've also learned one evening after locking my bike on high street (thinking it would be safer with constant foot traffic) so I could go to a film... So what I'm saying is don't go cheap. Buy good quality at Halfords or one of the online cycle shops like this one or this one (two of my favorites). Look at the rating it has and make a decision based on the security you feel you need rather than the price. (because a good lock will save you money in the long run!)
kryptonite is a well respected brand but they can be expensive. Sometimes you can find used ones on ebay however.
Good luck!

the first link i posted that didn't work

It very much depends where you are locking it, when and how long for.

For quick daytime trips around town & villages (skeepy, semi rural) I just use a lightweight combination lock that I can carry in my pocket. It's pretty uncommon around here for people to lock up bikes at all.

But In Central London overnight I'd want 3 D-locks and a prayer.

Thank you - will be cycling in the New Forest (where I imagine bikes get stolen) and along beach, stopping for a drink in a cafe but not much else. Won't be riding into town and leaving a bike for ages. Will have a look for locks and check my insurance, thanks for reminding me. Hadn't thought of that.

When I was a student in London the only locks the student union shop bothered selling were Squire Urban D locks. You can get them with an extension cable. Better a cheap bike and an expensive lock than a cheap lock and no bike!

Squire website