I think simplicity is often overlooked. Some web designers want to do things and add features just because they have the technical ability. I think a color scheme with no more than 3 colors is advisable and they should be of the same tone - sort of like decorating a room. Maybe you have 2 main colors and 1 accent color. For me, this also means that the text and background should be in colors that I can actually see - black text on white background works perfectly - no reason to mess with a good thing. Red or yellow text on a black background sends me running.
I think another problem with the design of some websites are that they use too many varying fonts. It really bothers me when there is a serif font on the same page as a non-serif. They just are not compatible together. I know this is subtle but it just takes away from the aesthetic.
I also think web designers forget about using heading tags: h1, h2, h3 etc. Not only does google like them but it helps to organize the page better for the user. It is much better to have headings generated from tags instead of images. Additionally, more paragraph breaks are often needed, not only for readability, but to just give the reader's eye a break. White space is very appealing to me, but I think sometimes people forget that less truly is more.
I have to say this is why HubPages appeals to me. It really is so simple in its design, yet so effective. I have also recently been using the Thesis theme for Wordpress and it really helps designers pull off very clean, fresh-looking sites. Can you tell I have a lot to say about this?