Best bag

What you're looking is sold right here at this web site:) Click the "Travel Store" tab at the top of this page. Here is a video with said bag and some basic tips on how to pack light:

Ah !!! the perpetual question. Rolling vs carrying, combination -- it is lot of personal preference. No best answer. We prefer the Rick Steves' carryon back pack. I think they are a great value for the money. We own three plus a much more expensive Eagle Creek that has more bells and whistles but don't use the bells. For a basic, carryon light weight bag it is hard to beat the Steves' bag. He has a combo but the wheels and handle add weight and reduce the space.

I want to pack light and take only a carry on.

In my opinion, that is inconsistant with a roll-on bag.

That somewhat depends on your airline. If you fly on a U.S. airline, they will probably allow you a lot of weight in a carryon. But I don't want to fly with a U.S. carrier.

On the other hand, if you fly someone like Lufthansa, you will be limited as to carryon weight. A roll-on bag, empty, can easily be half of your wight in this case. The net weight of your contents will be quite limited.

It does really depend on what you're doing and where you're going. Sometimes, a bag with wheels will be very helpful and other times, it can be a hindrance. Ideally, you might get one of each type of bag.

My favorite bag so far has been the Eagle Creek Switchback 22". It is a backpack with wheels with a zip-off daypack. To me, it's the most versatile carry-on size bag I've encountered.
http://www.eaglecreek.com/bags_luggage/wheeled_carry-on/Switchback-Max-22-20217/

That said, I also have 25" and 30" rolling duffles for times when I need to pack more, and a 22" backpack with zip-off daypack without wheels, when I need to pack extra light because I will need to carry the bag on my back more often than rolling it.
http://www.rei.com/product/770253

A rolling suitcase with backpack straps: High Sierra makes some good ones. But - it's not packing light. Whenever you add wheels to a bag, you add weight. if you think you will be rolling the bag more than carrying it on your back...check High Sierra out:

http://www.ebags.com/high_sierra/atq_carry_on_wheeled_backpack/product_detail/index.cfm?modelid=99765

http://www.ebags.com/high_sierra/at3_sierra_lite_22_wheeled_backpack/product_detail/index.cfm?modelid=63370

These have zip off daypacks...so you get 3 bags in one. A daypack, a rolling bag, or a bag that you can carry on your back.

Plan on the weight of the bag to be @5-8 lbs EMPTY.

Another choice is:

http://www.ebags.com/high_sierra/transport/product_detail/index.cfm?modelid=62988

This one has no wheels, but has a zip off day pack (handy for day trips) and hidden backpack straps.

Lindsay,
Check out the Osprey Porter 46. It is very well made and has received outstanding reviews from users. I also have another Osprey--the Meridian, with wheels and backpack carry-ability. The wheels are large enough to work on cobblestone streets in European cities, but I still prefer a travel pack without wheels. As others have said, wheeled backpacks weigh considerably more (7 pounds versus 3 or so); furthermore, the collapsable handle system uses up valuable packing space within an already-small the pack. Wheeled luggage works well for airport concourses; it works less well for Europe's city streets, train stations, or trains.

While you're at ebags looking at the expensive bags, check out their own "Weekender Wheelie." I own it and it's a good bag, however I no longer use it because I've stopped using wheels. It has wheels and backpack straps.

Weekender Wheelie

(It looks like they may be discontinuing it as they only have it in one color. There used to be five.)

Lindsay,

The 22" high Sierra rolled backpack is heavy. I got one about 2 years ago and even if like it in some ways, it's heavy , about 13 lbs with the day pack attached.Plus it's nor very roomy, the handle takes up the inside space.
I switched to a backpack. I got an Eagle Creek Explorer Trek model, 22" ,less than 3 lbs. Another good one is Kelty Redwing 3100 or smaller. The 3100 series is 25" long but very roomy.

My husband and I have the Osprey Porter and the Eagle Creek Explorer. They are both carryon size and we loved them! The ones with wheels were too heavy for us, although we don't have that much selection to choose from. I would strongly suggest you try them on in the store and don't forget to weigh them down. Not all backpacks fit the same and some are way more comfortable than others and this will vary from person to person.