By now, what should be abundantly clear is that: to each is own.  In regards to the front-end, I will actually concede that even ASP.NET is suitable if that is your strength (and you are aware of the licensing requirements, if you decide to extend Redmond's tech into your back-end). However, personally, I would go with either PHP (which is insanely popular in the Bitcoin community and extremely well supported) run over Nginx OR Node.js if you're comfortable using JavaScript and would like to assure maximum scalability on modest hardware.

Keep in mind that with ANY Bitcoin-related business, you will eventually have to tie back into the blockchain at some point.  There are companies like BitPay that do a very good job of abstracting a simple payment gateway over the blockchain and is a good solution if you're only looking to accept payments. However, if you need to manipulate the blockchain in anyway (like when sending coins) or integrate with it (like when you need to track transactions and confirmations) then blockchain.info provides a great API that lets you do this with little fuss.

If you decide to run your own back-end daemon (maybe for security reasons), you are certain to receive a lot of mixed advice as to the pros and cons of virtually every language, framework, platform, OS in existence (at least from the people on this thread). Stay away from Windows (at all costs) and go with whatever Linux distro you feel comformatable with (Ubuntu and CentOS are my favorites). There is an official C-based Bitcoin daemon as well as a very popular Java alternative. I'd stick with these for now as the others are very much unfield-tested at the moment.

Good luck!