For Online payment portals you can go for paytm.com or freecharge.com which will provide you all-in-one service phone recharges, phone bill payments, electricity, DTH recharges, bus tickets and water bills. Alternatively you can go to their official websites for online payments.
As for the PAN application, you can just visit the official website https://tin.tin.nsdl.com/pan/form49A.html and fill in the details, make online payment and the application is done.
Now-a-days it is very simple to apply for government documents online including TAN cards, Aadhaar card, passport application, business registration,etc. This can be a good additional service that you can offer.