Since September 2006 I have been working on the Open University (OU) course S103 Discovering Science, which I completed a few days ago. This distance learning course is intended to provide a foundation in science which will enable further study in particular areas, while also providing a broad overview of topics which are of interest to many. It covers biology, chemistry, physics and earth sciences in some depth, exploring such sub-topics as global warming, quantum mechanics, geology, DNA and RNA, polymers, and life on other planets.
The course is divided into twelve blocks, and comprises eleven textbooks and a collection of scientific articles for the last block. All blocks also have "study file" sections and multimedia videos and test questions. There are also optional local tutorials and online chat forums which are very helpful if you're stuck.
The course lasts about eight months, during which time you have to wade through the books and send in eight Tutor-Marked Assessments (TMAs) and a final End of Course Assessment (ECA). Study skills are stressed throughout, especially use of mathematics and equations, and essay-writing (my E2 experience certainly helped out here!).
The results from the TMAs help give you some idea how you're doing, and the online forums are good for keeping motivated. Discovering Science is a "level 1" course (roughly equivalent to first year at university) and completion enables you to tackle other level 1 science courses, or even the heady heights of level 2! I plan to study a level 2 course next - "Planetary Science and the Search for Life". I would heartily recommend study with the OU to anyone, but be warned - it is expensive. However, if you study enough courses, and we're talking at least four or five years here, you can gain an OU degree which is highly valued in the UK.