The most official list of mods you can get is maintained on the Minecraft forums in the Mods subforum, in the first pinned topic. The nice thing about using the forums is that you're going directly to the source – these forums are where the mod developers release their mods, so you're always sure to have the most up-to-date version publicly available directly from the author.
Currently, that pinned topic is:
... but the pinned topic's content and title is always updated to cover the latest Minecraft version, so don't let the very specific title worry you that it will become obsolete.
That thread's first post also has a link to an off-forums page where you can browse a sortable list of mods by various criteria such as which version of Minecraft it's compatible with, Forge compatibility, and so on, as a convenience for forum members and for easy updating by the list maintainers. The list is crowdsourced by fans from the release threads scattered around the forums as well as mods released off the forums, so it's extensive and rather high quality.