Links
Useful maths links:
Groups and Geometry in the South East, a series of meetings for geometric group theorists hosted by Cambridge, UCL, Oxford, Warwick, and Southampton
Jon McCammond's Geometric Group Theory website, especially useful for the list of upcoming conferences
The University of Illinois' Geometric Group Theory mailing list
How to Write a Part III Essay by Tom Körner, which is aimed at Part III students in Cambridge, but has some very good advice for general mathematical writing (and is an entertaining read)
The Mathematics Student Resource has links to a huge amount of advice on a variety of topics, including writing, publishing, grants, and interviews.
Useless links that you may find interesting:
Kenneth Falconer's maths poems (I particularly recommend A Poem of Academic Prejudice)