You also have to decide whether you want a retro/field-bag type of look or a modern sleek type look saddlebag.
I use a retro/camping look on my bike.
I have a Velo Orange banana bag for small trip uses.
I have a Rivendell/Baggins Little Joe for everyday stuff (medium)- they no longer make these.
I have a Carradice Nelson (large size) for when I ride with several days worth of clothes.
Carradice makes some great bags:
http://www.wallbike.com/carradice/ca...addlebags.html
You might like their Barley bag for normal use with room for a jacket, digital camera, tools and lunch, etc.