Where to look
If you are interested in a particular company, then the best place to look is that company’s website. Most companies have a dedicated Careers/Jobs page. You can also try the following job boards.
Here are a couple of blog posts which talk about the interview process and interview preparation.
Get that job at Google
Get that job at Facebook
I recommend getting a copy of Cracking The Coding Interview. It has a lot of interview-style programming questions which I found really helpful.
To get some more practice, you can visit the following sites:
A lot of people post the questions they were asked during interviews on these sites. These sites are, in some sense, a way to game the system because many interviewers ask the same questions again and again.
Finally, no amount of interview preparation can substitute for the hard work put in the class. So make sure you study your course materials well.