Looking at it that way, nerds aren't so much different from the other stylistically deviant highschool stereotypes like punks or goths. If you changed "blissfully unaware" to "aggressively resisting the fact", the definition would be pretty spot on.
When I think of a nerd, I think of this guy...
And if I were to think of an archetypical nerd, it'd be my man Steve. m-effin. Urkel.
So looking at these pictures, a common theme is oversized glasses, oversized, patterned button-downs, and poorly-fitting pants whose shortness is exacerbated by suspenders.
1. Oversized Glasses
[Via Urban Outfitters - $14]
[Sorry in advance to all my hipster friends reading this.]
These damn hipsters have ruined everything. I really searched everything I could, but couldn't find anything I liked unless I searched hipster glasses... and then I got angry. [the end]
A touch I see more on Halloween than anything is the tape around the middle of the glasses like they've been broken a couple times due to jock-on-nerd violence, clumsiness, or unwillingness to give up old glasses and buy something newer. I think this is more a cinematic thing and that that didn't really happen terribly often, so I'd personally advise against it. Wearing these glasses to begin with is extra enough already.
2. Oversized Patterned Button-Down
[Via Total Vintage - £9.99]
You can really find these anywhere, but if you want my opinion, I'd suggest the clearance racks at Macy's, Marshall's, or TJ Maxx. The pattern doesn't even really have to be this crazy, just very bold and obvious, like Urkel up top.
Also, always tuck that bitch in. It makes the outfit.
3. Poorly Fitting Pants
[Via Dockers $24.99]
The pants should be a simple pair of carpenter's jeans or unmarked khakis. Like the button-down, you can find these anywhere. I'd personally suggest Walmart. Note that the particular pants aren't remotely close to as important as the fit and how they're worn.
The cuff of the pants should not go below the top of the shoes, allowing the pants to be pulled up high, showing most of the sock.
4. Suspenders
[Via Duluth Trading Co. - $16.50]
These aren't completely necessary, but they're usually a nice touch. If you wear suspenders with an outfit like this, make sure they pull your pants up nut-bustingly high or you might inadvertently look [i]less[/i] nerdy.
5. Athletic Shoes
In my opinion, one of the easiest ways to make a fool of yourself in public is mixing athletic shoes with dress clothes. Nerdy clothes are generally considered "dress" clothes- the only reason they don't look it is the fit.
And though our archetype, Urkel doesn't do it in the picture I selected, I see enough engineers and old professors doing it on a daily basis to prove my opinion.
As for suggestions, I have a religious hate for new balances, but if you really want to go balls out, buy a pair of shoes that look like the ones above from Payless. You're looking for something with a lot of texture, patterns, and random ugly stitching, 10 extra points for velcro.
And there you have it. I wouldn't suggest you wear this, but I think, like the hipsters, that taking bits and pieces from a relatively shitty style can help you make something new.