from <http://weblog.jamisbuck.org/2007/1/31/more-on-watching-activerecord>

In config/environment.rb:

def log_to(stream)
  ActiveRecord::Base.logger = Logger.new(stream)
  ActiveRecord::Base.clear_active_connections!
end

then in the console :

>> log_to STDOUT
=> ...
>> Post.find(:first)
  Post Load (0.000138)   SELECT * FROM posts LIMIT 1
=> #<Post:0x1234 ...>
>>

The best part is, by clearing the active connections after setting the logger, you can change the logger at any time, even after you’ve made any number of find calls.

And, you can pass your own stream objects into it:

>> buffer = StringIO.new
=> ...
>> log_to buffer
=> ...
>> Post.find(:first)
=> #<Post:0x1234 ...>
>> p buffer.string
=> "  \e[4;35;1mPost Load (0.000138)\e[0m   \e[0mSELECT * FROM posts LIMIT 1\e[0m\n"
>>