Picassa allows you to organise your images on your hard drive and then work on them individually too - it's perhaps the easiest for a novice to get to grips with and allows you to tinker with images without damaging the originals. It's made by Google.
Irfan View is the one application that is almost always open on my system - I use it to view all my images on the memory card, to preview and find images, sort and organise. It has lots of amazing features and I'd part with a lot on my hard drive before you could prize that from my cold dead fingers! Despite its simple appearance, it has a lot of very sophisticated features and even allows you to install and use Actions designed for Photoshop compatible applications - which makes it a pretty powerful tool in your arsenal.
Fast Stone Viewer is incredibly similar to Irfan View.
Gimp is fairly new to me and I've not used it much myself, but I know from the people whose work I rate that recommend it, it must be worthy.
XnView is another I have open often. I use it alongside Irfan View as it's similar in functionality, but different enough in the GUI that I use it for slightly different things. I was very impressed when I had a problem with a feature that didn't work as I hoped and would like, I went to the site forum to ask about it (thinking that I was just doing it wrong) and the application creator changed the program for me - actually re-wrote it to do what I wanted. A feature I use very often, with gratitude.