Being able to take your pencil marks up off the paper is as important as being able to put them on in the first place. In my years of drawing, I have settled on two main types of erasers and use both for different purposes. Both are very inexpensive.
The best eraser if you are working on rough paper or doing a lot of work with soft pencils is a gum eraser, or kneaded eraser. It costs a dollar or two and looks like grey clay. If it gets dirty, knead it and work it and it will come clean again. You can form it into a small point for taking up small areas, or a big broad blob for erasing large areas. It is gentle on the paper.
The best eraser if you are working on smooth paper or with hard pencils, is a white vinyl eraser. Good ones are made by Staedtler Mars, and also only cost a dollar or two. They are used by draftsmen. A white vinyl eraser is rectangular with sharp edges and a cardboard cover around it. Used carefully, you can erase large areas cleanly and it does a good job picking up pencil marks. Wipe it off on an old T-shirt if it needs to be cleaned, tissue works well too.
Another drafting tool that is really good for art is an eraser shield. It’s a thin piece of metal with various sized slots in it, and it’s very good for erasing exactly where you want to, and no more. This, too, is also available at most large office supply stores.
If you want to check out a great selection of art supplies, DickBlick.com is the place to go.
Mindflight 