- Javascript, Javascript, Javascript
- Frontend: Backbone / Angular/ whatever MV* framework takes your fancy
- Backend: restful web services, good APIs. MVCs like Rails/Django if you can't push that stuff to the client.
- CSS pre-processors (SASS, Less, etc). Using classes instead of IDs, for modular, re-usable css. OOCSS ideals and methodologies.
- Dependency management via AMD / requireJS.
- Templating (underscore, dust, hogan, etc.) be it client or server-side.
- Page performance (PageSpeed Insights, Chrome Dev tools, etc) - to get content on the page ASAP, in seconds. On that note, to keep up with the Velocity web perf conference.
- Monitoring and Analytics - Real User Monitoring, Synthetic Benchmarks, A/B testing, Dashboards
- Fast development pipelines through something like Mimosa