mathigon — Philip Legner’s beautiful web site on maths
plus magazine — an online magazine dedicated to explaining mathematics
madras college activities page — madras college is a school in st andrews with what looks like a good maths department
number gossip — everything you wanted to know about a number but were afraid to ask!
a mathematician’s lament — Paul Lockhart on what is wrong with the way maths is taught in the USA but could equally be said of here
interactive and dynamic
cut the knot — good for interactive puzzles
geogebra — dynamic geometry for everybody
numberphile — videos about numbers and stuff
3brown1blue — for Advanced Higher topics and beyond
quotations on the subject of maths
today in science history has a page of mathematics quotations
how to become a quant
Michael Halls-Moore has a very informative site on all things to do with becoming a quantitive analyst. See A step-by-step guide on getting a job as a quantitive analyst and Understanding how to become a quantitive analyst. Basically you have to be prepared to study a lot of maths.