Before I choose the first / only JS GUI library I know, I’d like to see what else is there on the market.
Reason: For my taste, Ext.js has a too strong “Windows XP” touch which looks really weird on a mac. Mac users are my target customers, so maybe there’s something out there that suits this much better or is more neutral.
Needed: A customizable GUI JavaScript framework especially for “intelligent” forms and form functionality (validation, pleasing visual feedback), Ajax roundtrips (i.e. checking if a user name already exists), sophisticated input fields like those from Ext.js, where you can also start typing in a dropdown to search through (similar to word processors where you type in a font into the font selector dropdown), etc.
Most importantly customizable: My entire page is in black/silver/white style so it would be great if it was possible to develop own skins and graphics for it.
List of some Javascript GUI libraries (not ordered):