What's good, no viruses / adware checker and disposal program?

Where can I get something that will detect viruses and adware and remove them? I'm looking for something that people have tried because I have not had any luck with the download so-called anti-virus before. They either add virus rather than get rid of them, or they claim to be free, find 500,000 viruses, and tell me I need to pay a lot of money to get rid of them. So what is a legitimate site that will find and remove, free of adding virus / adware on my computer?

AVG