I really liked the Edie Bauer Mini Bag, I went through two of them, actually I still keep one in the car with a change of clothes, toys etc, just in case of an emergency - DD has been potty trained for about 6 mos.
Last disney trip I bought the Mini Sling Bag from REI, it is a little bigger than a purse but it is a sling style backpack. I loved it so much I started using it everyday as a diaper bag. Now I use it when I have to take DD to meetings, or for a day at the fair or whatever. I mentioned she is potty trained but still I like to have a change of clothes, wipes, disposable bibs, tippy cups, etc. I travel pretty light, the sling bag mignt not work for 3 kids. But it is easy on your back and with the diaper bag on your back it is easier to manuver the baby in your arms, rather than having an actual diaper bag over one shoulder, kwim?