Intelipurchase.com allowed customers in different credit brackets to purchase a computer on credit based from different manufacturers on a single site. One of the first projects for us where we needed to hand off the complete site, SQL database, etc to a different server. It makes you more conscience of developing a really flexible, bug free system. You also have to make sure to include tools to update settings that would normally just be a line in a constants file.

SQL (Stored Procedures), ASP (VBScript), JavaScript