But to throw what others have said out of the water, I went without a tie once and got the job.
All depends what the company are looking for. For example, going to a Virgin interview without a tie could be counted as extra bonus points as Mr Branson doesn't like them.
I don't think I have ever worn a jacket, and wouldn't hinge a success/failure on whether you wore one or not. I tend to wear nice trousers (IE, proper "work" trousers) and a shirt / jumper combo; a nice jumper though, doesn't have any brand name or crazy design. Sometimes a tie, sometimes not. If a 2nd interview, usually no tie.
Don't wear trainers - even if they're plain black "plimsole" type.
Don't wear uniform. I have attended two interviews in the past with two candidates that wore their uniform - one even had their badge attached. It's not that you look poor and can't afford a different set of clothes, it looks more like you don't really have any other life apart from work.
The single most important factor in any interview, in my opinion, is getting the interviewer to like you. If there were two identical people (in terms of knowledge), one in a suit, one that is in a smart jumper/shirt/trousers combination, but the latter made a better impression, I'd bet my wage they would get the job.