Can you recommend "expense management" software for a small business?

Does anyone have any recommendations for software for small companies to manage employee purchases, reimbursements, approval, receipts, etc?

For example, if I want to attend a conference, buy computer equipment,
etc, I need to get approval for the purchases. Then I submit monthly
receipts (either hard or soft copy) for reimbursement. It becomes
confusing to manage all the little slips, who’s approved for what,
etc. We’d love to have a nice little web app to do it for us!

Any recommendations?