Here's a couple of ways that work for me:
1. I have a Today perspective that consists of: View Mode: Context, Context Sidebar Filter: Active, Group Actions By: Context, Sort Actions By: Due, Status: Due or Flagged, Duration: Any, Flagged: Any. I use the flag like the star in Things - for manually highlighting something I want to do today. For me, this works on my iMac exactly the same way as the Today focus in Things worked. The only problem with this perspective is that my Today perspective on my iPod Touch has some additional tasks that are inactive, even though my context filter is set to Active. So I came up with:
2. My "All Available" perspective, which is really a Today list "plus," but it also works for me as just a Today list with the bonus that it appears exactly the same on my iPod Touch as it does on my iMac. My settings for this perspective are: Context, Active, Flagged, Due, Available, Any, Any. What I end up with at the top of the perspective is all of my Flagged tasks with the most overdue task first through the tasks due today followed by flagged tasks without due dates. Following that section are all of my Unflagged tasks, again with the most overdue task first through the tasks due today + my bonus section which is the rest of my active tasks starting with those with due dates that have not arrived yet and ending with active tasks with no due dates that are sorted by the order of folders and projects in the sidebar. I now use this as my Today list because what is really my Today list is at the top of the perspective list and I can ignore what is below it, or I can peruse the rest of the list if I have some time available but not enough time to do anything on my Today list - or if I just need to do something else right now.
For me, it has become my favorite perspective when I am in the "doing" mode - and it works on both the Mac and the iTouch.