This is late, but since this topic is the first search result of google for godot export hints, and I ask google for this hints a lot, i will re-answer that only for googling pourposes:
new hints docs:
http://docs.godotengine.org/en/latest/getting_started/scripting/gdscript/gdscript_exports.html#doc-gdscript-exports
Godot exports hints at oct-19:
If the exported value assigns a constant or constant expression, the type will be inferred and used in the editor.
export var number = 5
Export can take a basic data type as an argument, which will be used in the editor.
export(int) var number
Export can also take a resource type to use as a hint.
export(Texture) var character_face
export(PackedScene) var scene_file
There are many resource types that can be used this way, try e.g. the following to list them:
export(Resource) var resource
Integers and strings hint enumerated values.
Editor will enumerate as 0, 1 and 2.
export(int, "Warrior", "Magician", "Thief") var character_class
Editor will enumerate with string names.
export(String, "Rebecca", "Mary", "Leah") var character_name
Named enum values
Editor will enumerate as THING1, THING2, ANOTHER_THING.
enum NamedEnum {THING_1, THING_2, ANOTHER_THING = -1}
export (NamedEnum) var x
Strings as paths
String is a path to a file.
export(String, FILE) var f
String is a path to a directory.
export(String, DIR) var f
String is a path to a file, custom filter provided as hint.
export(String, FILE, "*.txt") var f
Using paths in the global filesystem is also possible, but only in scripts in "tool" mode.
String is a path to a PNG file in the global filesystem.
export(String, FILE, GLOBAL, "*.png") var tool_image
String is a path to a directory in the global filesystem.
export(String, DIR, GLOBAL) var tool_dir
The MULTILINE setting tells the editor to show a large input field for editing over multiple lines.
export(String, MULTILINE) var text
Limiting editor input ranges
Allow integer values from 0 to 20.
export(int, 20) var i
Allow integer values from -10 to 20.
export(int, -10, 20) var j
Allow floats from -10 to 20, with a step of 0.2.
export(float, -10, 20, 0.2) var k
Allow values 'y = exp(x)' where 'y' varies between 100 and 1000 while snapping to steps of 20. The editor will present a slider for easily editing the value.
export(float, EXP, 100, 1000, 20) var l
Floats with easing hint. Display a visual representation of the 'ease()' function when editing.
export(float, EASE) var transition_speed
Colors
Color given as red-green-blue value (alpha will always be 1)
export(Color, RGB) var col
Color given as red-green-blue-alpha value
export(Color, RGBA) var col
Another node in the scene can be exported, too.
export(NodePath) var node
Bit Flags:
Individually edit the bits of an integer.
export(int, FLAGS) var spell_elements = ELEMENT_WIND | ELEMENT_WATER
Set any of the given flags from the editor.
export(int, FLAGS, "Fire", "Water", "Earth", "Wind") var spell_elements = 0
Exporting Arrays:
Exported array, shared between all instances. Default value must be a constant expression.
export var a = [1, 2, 3]
Exported arrays can specify type (using the same hints as before).
export(Array, int) var ints = [1,2,3]
export(Array, int, "Red", "Green", "Blue") var enums = [2, 1, 0]
export(Array, Array, float) var two_dimensional = [[1.0, 2.0], [3.0, 4.0]]
You can omit the default value, but then it would be null if not assigned.
export(Array) var b
export(Array, PackedScene) var scenes
Typed arrays also work, only initialized empty:
export var vector3s = PoolVector3Array()
export var strings = PoolStringArray()
Regular array, created local for every instance. Default value can include run-time values, but can't be exported.
var c = [a, 2, 3]