CCleaner is an amazing program, not just for Registry cleaning (which typically doesn't really do much at all), Defraggler is a great program to have, seeing as the windows defragger is fatally flawed IMO.
I'd also suggest the program Malware Bytes, it does some pretty good scan-work, and misses things a lot of virus protection programs miss. Also, I would suggest Spybot Search and Destroy (Spybot S&D), it's a pretty good program that can keep viruses at bay, and if you dont have virus protection, I'd throw Avast! on top of that.
I use all of these, and they work great for me. :3