How to use

1. Look at any thing (block or entity, the sky doesn't count)
2. Press I (rebindable)
3. ???
4. profit

The title of the waypoint is the display-name of the block or entity you are looking at, except for traders — the waypoints will have their 'type' in the title instead.
For example: look at copper bits, press I: a waypoint will be added with title “Copper bits (…)”, with an orange pickaxe icon. 

Please keep in mind that the current version is not play-tested properly. The color scheme is based off the colors that would be rendered on the (colored) map, with some values set manually for usability. This should still save you the annoyance of opening the map to punch in the same old information. When you're waiting for the night to pass, or for the food to cook — revisit your map, recolor and rename your waypoints as necessary.

Also

Consider rebinding the shortcut to ALT+Q. I've been playing with this mod on for a bit, and it “fits my hand” when playing, so to speak. I may eventually change the default key-bind.

I noticed that meteoric iron has the rock icon instead of the pickaxe icon, must be because it's classified as rock instead of ore in the code. I'll fix this eventually.

If you find any issues or have suggestions, please give me a comment, and I may make changes. 

FAQ

Is this a client-side mod?
Yes

Does this work in multiplayer?
The action is functionally equivalent to adding a waypoint through the map UI.

Why?
Because I have terrible memory, and I can't remember how many times I forgot about something being somewhere. This extends to real life…

Support for multiple languages?
Yes, the waypoints added will use your current language.