I have used both Certify.com and Concur.com as SAAS expense management. They both have good apps for both Android and iOS (Concur even had a Windows Phone App for a while that worked very well).
When I used Concur I traveled a fair amount for work, so I can truthfully say, just having the ability to take a quick pic of your receipt doesn't mean it will happen. Every time I traveled I would end up at the end of the trip taking pictures of all the receipts I collected. However, I used the app to do so, much easier than doing it on a PC.
Both of these can classify expense if you need to separate them out for accounting and they can even cut a check for you or integrate with your payroll software.