ICANN has made available a range of statistics and pretty graphs that allow you to see easily what’s going on with the various registries it is responsible for. (ccTLDs such as co.uk and .fr are not included for this reason)
Full details of the updated system they’ve made available may be found on the ICANN site, but if you just want to “jump right in” then you may want to go here.
All of the data regarding registry statistics is made available in other formats, but having it all nicely prepared and graphed helps get to grips with it.
NB: You’ll need Flash to view the graphs and there doesn’t seem to be any way of re-using the data at present