some salesforce web to lead development resources

How to obtain a field ID
http://salesforce.phollaio.com/2007/04/02/how_to_obtain_a_field_id/
You can find a list of all SFDC standard Fields and also some information about custom fields.
Very handy and helpful

Validation Rule formulas: Part 1
http://salesforce.phollaio.com/2007/01/08/validation_rule_formulas/

Validation Rule formulas: Part 2
http://salesforce.phollaio.com/2007/01/10/validation_rule_formulas_part_2/

Play with Custom Links: Part 1
http://salesforce.phollaio.com/2007/01/16/play_with_custom_links/

Play with Custom Links: Part 2
http://salesforce.phollaio.com/2007/01/31/play_with_custom_links_part_2/

sfdc-web2anything
http://salesforce.phollaio.com/2008/11/26/sfdc-web2anything/

Introducing an open source object "sfdc-web2anything "
http://code.google.com/p/sfdc-web2anything/