i first looked at hecl, and it looks alright for a programming language site
there are a few easy things that would make the site look and feel above-average:
(1) behavioral: a click on the orange box should take you to / - logos are links to the home page by convention, and users (and me) get confused, when they are not
(2) style: make the relation between navigation and content clearer by
(2.1) adding whitespace between the orange box and the actual content, so that it becomes clear that navigation and content belong together
(2.2) extend the highlight of the current navigation item to the far right of the navigation box, so that it "touches" the content (tabs are always "connected" to their content, and you're basically doing vertical tabs here)
(3) get rid of the "links" headline and the bullet points in the navigation (css is your friend there)
(4) whitespace is your friend, even in the example images - the right example looks very crowded. read the osx interface guidelines (or, less preferrably, the gnome one) for examples of good interface
(5) distinguish _somehow_ between internal and external links in the navigation. i first thought that that was the difference between bold and non-bold entries in the navigation - but apparently, it's not.
disclaimer: i'm not a designer by trade, this is just what i picked up during my studies (independently and on university) and by working together with designers
if you want a good introduction to design and a good read at the same time, read "design of everyday things" and look for slides of user interface design lectures - many teachers put them online!