ArcView's Help: Sample Scripts and Extensions
ArcView's System Scripts
ArcScripts (from ESRI - go to Avenue or ArcView links)
Columbia Mapping (follow links to Scripts, Extensions, and Dialog Designer examples)
Stuff for ArcView Users, Mark Cedarholme
ArcView Programmer's Reference (Gary M. Greenberg - a searchable script repository)
GIS at the Center for Social and Community Development, Rutgers University (look at scripts link, and check out the movies using ArcView maps)
GIS Tools (ArcView Extensions for Spatial Analyst from the USGS Alaska Biological Science Center)
Oregon Department of Forests - State Forestry GIS Tools (Extensions, including the XTools Extension)