# terminal
script/server -u

# /some/view.erb
<% debugger %>

# open the url associated with that view, and switch over to the terminal to play with ActionController methods and objects
(rdb:2) request

The 'request' and 'response' objects are chock full of useful info.  But console can't usually access them.  Here's how:
start the server with the -u option, insert a breakpoint where you would like to have access to the controllers/helpers/etc.  When finished, just type 'cont' to continue execution

Call ActionController methods from the Rails console

debug, rails

Rails