I have just been looking for tyres and been trying to find some good brand tyres at reasonable price. I know they are all round and black but those four patches of rubber are the only thing stopping you disappearing into the undergrowth. For me cheap tyres may save money but can cost you dear if they fail you in emergency situation. Some cheap tyres in independent tests can take 10 meters longer to brake a car to standstill in the rain. Pace out 10 meters and think where you would rather stop. Auto Express have for a number of years done very in depth tyre comparisons with some links on where to buy them from. For details check this link;
http://www.autoexpress.co.uk/products/total_tyre_guide/213177/tyre_test.html
They also suggested some buying tips. Firstly, ring around local suppliers and see if they will 'move' at all. Internet dealers often link up to local garages who will install them once delivered. Some even install at work or at you home. It depends on your life style really. Here are some internet dealers again check and compare but less frustrating than lots of phone calls.
http://www.tyrefitdirect.co.uk/
http://www.valuetyres.co.uk/default.php
http://www.tyreplus.co.uk/home.asp (who guarantee they won't be beaten on price)
Good Luck and now is the time to check tyre depths before winter snows and heavy rains.