How do you find Item IDs?

[beefspace]

Trying to find the dew collector item ID. I though the XML files in the data/config folder had this stuff but I cannot find anything.

[Shurenai]

If you're searching for the Id to do the give command, it's infinitely easier to enable creative mode using the 'cm' command, exit the F1 console, and press U to open the creative menu; That menu has a search field near the top that lets you simply search by name whatever item it is you're after. Just be sure to disable it again if you care at all about achievements.

[seven]

Dew collectors have a name but also a number. I imagine all things do. Shurenai's advice is the easiest if you know what the item you're looking for is called, but it's possible to get the name, and number, if you don't.

Enable debug mode in the console with 'dm'.
Back in the game press F3. This will display several panels of information.
Look at the dew collector, or other thing, and hold down Shift.
In the Focused Block panel it will now show "id=18758" and "Name:cntDewCollector", and searching on either of those will find the the item in creative menu.