Here are some of the Butterfly/Lepidoptera websites and resources that are useful.
UK Butterflies
UK Butterfly Conservation: Butterflies
UK Butterfly Conservation: Moths
UK Butterfly Conservation area branches
British Lepidoptera by Chris Lewis
Butterfly Conservation Europe
The Wildlife Trusts: How to identify Butterflies
The Wildlife Trusts: How to identify Moths
The Wildlife Trusts: How to identify Caterpillars
UKmoths
Simon Wates Algarve Butterflies section of his Algarve Birdwatching site