It depends on which Marketo Package that you have. If you go to the analytics section each one of the icons represents a type of report that you can get and for the most part it's pretty self explanatory. The top 3 I use the most in MLM are email performance, email link, and leads performance.
Email Performance - opens, clicks, unsubscribes delivered, bounced,etc
Email Link Performance - how many clicks broken out per link
Leads Performance - Group leads by a variety of factors including Source, Status, Month created, campaign, etc.
Web Page Activity
Landing Page Performance
Engagement Stream Performance -
Company Web Activity
Sales Insight Email Performance
Opportunity Influence Analyzer (I use this a lot to dissect deals) Not sure if this comes in all editions. Is there a particular reporting question that you have?
There is also a lot of data that you can put together just by using smart lists and filters so the possibilities are really endless.
thanks Jessica - I agree I think that a lot of information can be obtained via smart lists (and provides details on the leads vs. just the numbers).