There are many sites where you can explore Mathematics beyond your school syllabus – try some of these:
Maths Careers this site, managed and maintained by the Institute of Mathematics and its Applications has extensive information on careers in Mathematics and applications of Mathematics in everyday life. Note the various tabs such as Science and Engineering at the top of the page and pages for various age groups, see 11-14 for example.
Nrich (note you can search for a topic)
Mathematical Moments an extensive collection of pdfs on many different topics in science, nature,technology, and human culture.
For older students:
Reading list from Cambridge which should interest any student of Mathematics
STEP (university admissions papers)
STEP – Worked examples