when i stand up on the pedals there is a creak?

Bazza,
I bet it is your bottom bracket.Depending on age of bike probably does not need replacement,just adjustment and fresh grease.Different types of BBs will make creaking noise when either too tightly adjusted or too loose.

Lazza
November 2009

first thing-

check that your cranks are on tight. the crank arm is what the pedal is attached to. Where the crank enters the bike is called the bottom bracket and there is usually an 8mm hex nut there that may need tightening. Also, check the condition of your pedals by trying to lift them up and down "in place". There should be no movement. pedals are pretty cheep to replace and need replacement every few years.

dan
October 2009

the ballberings ring in the crank might have broken up , you need to open the bottom bracket on the adjuster side , after you have takeing off the peddel arms, get two new ballbering rings £2 each , grease the up well , put everything back , and test them out, now if your useing cycling shoes check the cleats, for movement ,

mick
October 2009