When planning what to take in your tool kit you need to bear in mind what problems you are likely to encounter and also which of these problems you are going to be prepared to tackle yourself - there is no point packing tools like Torx sockets for stripping the engine unless you actually need it.
The golden rule when buying the tools is Don't buy cheap tools! There are lots of cheap tool kits on the market that are generally pretty poor quality, the last thing you want is the tools breaking on you. Ideally you should try to buy professional level tools that are guaranteed for life - in other words they are built to last.
There are a lot of professional tool manufacturers out there like Snap-On, Sealey, Draper, Lazer, etc who produce some great kit used by most mechanics and then on the other hand you have companies like Halfords and Machine Mart producing their own professional ranges which are generally not too bad - I actually find the Halfords ratchet spanners invaluable in the workshop.
If you have the time and patience, keep an eye on eBay because you occasionally find professional mechanics selling their tool kits and there are some great bargains to be had - I have seen £8,000 of Snap-On tools going for £500 - with life time guarantees it doesn't matter how old they are.
If you can't find a bargain on eBay, companies like Sealey,do starter kits, or toolbox deals where they bundle a collection of the most common tools into a tool chest as a promotion which provides a great starting point - ask your local Motor Factors if they know of any of these promotions - actually ring around all the local Motor Factors to find out what manufacturer's tools they sell and what deals are on
The links on the left will take you to the lists of tools and consumables.