I built a pretty expansive ecommerce platform. This is what it included (kind of categorized):
Orders, revenue, average order, average revenue
Top search engine search terms, top referring search engines, conversion rates of search phrases
Top pages, top referrers, top user agents, total visits, visit duration
Top products ordered by quantity and revenue
New customers, first time buyers, total number of registered users
Top in-site search terms, conversions of those terms
Visits to order, cart views to order, checkout initiations to orders
I didn't include this overtly, though it can be done by putting two reports together -- Top customers by total expenditure and by order frequency
