I think it depends on the company, if you know they're a very casual place (like a startup etc..) then don't worry about it but otherwise you're probably not going to go wrong in general with a shirt and tie as most others have suggested in the thread.
The other important things are to consider things like lighting, where to position your camera, test it out yourself to make sure you can be clearly seen. check your microphone too in say a test call with a friend or family member, I don't think it's ideal for example to be hooked up to some hands-free kit etc... Better to isolate yourself in a room for the interview and ask anyone else in your household in nearby rooms to keep any noise to a minimum etc.. consider buying an external mic so you can be heard clearly.
As someone else mentioned, look at the camera, make sure to test your connection etc.. on the day and be ready a bit before the meeting, worth having some notes and your CV, job description available as someone else mentioned re: their multi-monitor setup, you could always print some of that stuff out too or have it on a tablet, if you're referring to it during a chat with them you can look organised pulling a tablet or folder out and openly be seen to be referring to that stuff instead of perhaps having your eyes looking distracted/away from the camera.
Also, have a notepad ready as you might in a face-to-face interview as you can still take notes during the Q&A etc... with an actual notepad or just on a tablet.