Good question. Geocoding is often a bit difficult to integrate, at least from my experience... it'd be nice if you could just plug it in and have it work right away (without having to consign oneself to an integrated map service, like Mapquest, etc).
I'm assuming your web app uses Javascript, and some server-side code of any platform.
I work at SmartyStreets where we perform address validation and geocoding. Our service, LiveAddress geocodes addresses, but because it's CASS-Certified it also verifies that the addresses are correct and valid and will standardize them if they are not (something that Google/Mapquest do not do).
Since you'd rather not be constrained to a particular map provider, I'd suggest a service like LiveAddress which you can switch out anytime and remain totally transparent to your front-end. It's an API you can hook into easily from any platform/language, and it integrates seamlessly with Javascript because the output is JSON.
If you care about speed and reliability, it's good to know that LiveAddress is geo-distributed, with guaranteed uptime.
It's free to sign up and start using indefinitely, so if you need a quick-fix, that might do it for you. If you have any other address/geocoding-related questions, I'll be happy to help.
