Jeans. Can never find a pair that fit perfectly, are the style or colour I want and don't cost the earth.
'Going out' sandals - a combination of the right height heel so they look flattering but I can still dance in them, comfortable enough to walk home in, straps that don't dig in or rub and they have to go with more than one outfit to get my moneys worth out of them.
Appliances like washing machines, fridge freezers etc. - so many different features to consider and will I use them all? Will I regret not having a certain feature or the next model up?
Christmas presents when you don't know what to get - the endless browsing between shops looking for inspiration.