Some useful websites:

UK Morris Dancers - useful for finding a Morris side near you, and lots of other information
The Morris Federation
The Morris Hub
The Horsham Morris Tradition - a ten-minute YouTube video featuring lots of dance clips, and quite a range of Morris sides, including one on the other side of the globe!

Some Morris sides we like (but if a side is not listed, it doesn't mean we don't like them!)
The Wild Hunt Bedlam Morris - based in Croydon
Mayflower Morris - Ash Vale, Hampshire
Mad Jacks Morris - Hastings, Sussex
Shrewsbury Morris - based in, you guessed it, Shrewsbury
Alton Morris - Alton, Hampshire
Hook Eagle Morris - Hook, Hampshire
White Rose Morris - Huddersfield, West Yorkshire
Sound and Fury Morris and Sword - Seattle WA, USA
Black Joak Morris - Sydney, Australia