I dont know if this has been mentioned, but a sound system would be great. The ability to implement music and sfx is just a little thing that would be cool, but i dont know if it is really necessary for a level creator.
I think you're the first to mention it, but I like the idea! A tiny bleepy-bloopy piano or something would be cool.
That sounds great
I second this :D
Either provided or upload-able, it will be a very nice touch!
I think it would be fun to have one built-in, but maybe that's just because I like building stuff ^_^;