I am a solid Programmer and I know pretty much all I need to know about Backend- and Frondend-Developing.
But I would like to get deeper into the Design-Aspect. I am not talking about HTML, CSS, etc.. More about what makes a good Design actually a good Design. I already read "Don't make me think" and "The Design of everyday things", but they were more about usability then actually what makes a design beautiful.
Any recommendation what (online-)sources I should try to teach myself?
You might want to try <a href="http://teamtreehouse.com/" rel="nofollow">http://teamtreehouse.com/</a>
They have some good videos that give concise explanations on a range of topics including design.<p>I would also try looking at <a href="http://dribbble.com" rel="nofollow">http://dribbble.com</a> for inspiration even though it is not an official learning resource it is valuable.<p>For books dealing with good design I would recommend "The Non-Designers Design Book". It is general advice but you will be surprised at what a huge difference it can make. Its a great foundation to build upon.<p>If your really motivate, buy some books on color theory, typography, iconography, and layout. These are all the essential building blocks for design (web and print).<p>Finally if you need to brush up on your photoshop skills, try psdtuts.com for some good tutorials.<p>Good luck.