Shoulder bag alternative for camera backpack

I have a Lowepro Flipside 300, and I like it a lot, but it's pretty impractical on a long trip when you also have a large backpack to lug around. For my next trip I need some kind of a shoulder bag for my camera equipment, since I have to carry a large backpack on my back.

Currently I can fit the following equipment in the Flipside 300 ( http://products.lowepro.com/product/Flipside-300,2083,14.htm ):

1. 5d Mark II
2. Canon 70-200 2.8 IS lens
3. Canon 24-105 L IS
4. Sigma 50 2.8 Macro
5. Memory cards + Filters + misc. in the top compartment
6. Filters/memory cards/remote/misc in the movable compartments.
7. LCDVF Loupe

Could someone recommend good shoulder bag alternatives which fit about the same equipment (but not less) that the Flipside 300 and which are practical to use (i.e. not very bulky or heavy) with a sufficiently comfortable strap?

Thanks!