Personally, I've always done the whole suit and tie thing. Maybe a colored shirt and a patterned tie. But I've also given interviews to people wearing business casual and I really don't care about that either way. I wouldn't do a t-shirt and jeans, but from what I've seen - in the US at least - it's not as big a deal in the tech world. I've even had companies tell me that if I showed up in a tie they'd make me take it off.
Like someone else here said, go mainly for comfort, but I'd add don't go for so much comfort you look like you're on a vacation at the beach or something.