UKC

While questing about on a tick list I came upon a couple of pairs of perfectly matched 3 star routes sitting side by side, aptly named and and complete antithesis of one another in nature of climbing ...real yin and yang pairs ...each made better better by the presence and absolutely contrasting nature of the other...i had never noticed this before
...excuse my metaphors for their nature...

Heaven Crack, Stanage Popular...creamy chocolate flowy bit of climbing
Hell Crack, Stanage Popular...a nut crunch where you feel you could break a tooth

Heaven Crack, Burbage North...Crack climbing for the digital age
Obscenity, Burbage North...Analogue with a flutters of white noise

Any others to be recommended?

Theres a classic odd pair on the Idwal Slabs:

Ordinary Route (Diff) - straightforward , well protected.

Hope (V Diff) - devious, slippy, twisty, precarious

Moon Walk (E4 6a) and Moon Crack (E5 6b)

Not strictly side by side now: Chequers Buttress (HVS 5a) and Chequers Crack (HVS 5c)

Do they have to be close in grade?

How about Heather Wall and CMC Slab at Froggatt?

Better "pair" is Heather Wall (jamming joy) and Silver Crack (only joyful for masochists ).

Presume you mean Amazon Crack @Burbage North

I thought they had to be adjacent (aside from eliminates). 

There's only an "eliminate" slab between them

Edit: For people operating at that grade, they are effectively adjacent so I think that's ok within the OP's criteria.

Oh yeah ...my bad. Pretty much adjacent. 

Not 3 stars but Pathos (E3 6a) and Lithos (HVS 5b) at Brimham Rocks are two very good side by side routes one being a crack which runs out before the finish the other a fine balancy arete.

How about Adam and Eve at Shepherd's? Three star VS's next to each other, the one strenuous and well protected, the other delicate and bold.

Still to do either, but I believe they are very different:

Raven's Gully (Summer) (HVS)

Raven's Edge (Summer) (VS 4c)

Well, talking of Brimham how about the adjacent routes with antithetic names: Charming Crack and The Brutaliser. (Actually, they're both brutal.)

How about:

Cameo (E1 5a) - a little balancey, generally steady, but long and bold and refreshingly heady. One often taken on by aspiring E1 leaders, who find themselves suddenly understanding the nature of commitment, as they run it out above small gear...

Central Route (E1 5b) - just around the corner, at the same grade. Pleasing holds and well-protected, but steep and sustained, with move piled on move; and you're suddenly in over your head, as you fight against the burning pump and the rising panic...!

I always quite liked the original ying and yang at whitestone cliff. Fashions change though , it only has 7 logbook entries on here.

Older again but still justifably popular , how about cenotaph corner and cemetery gates?

And if White Slab was one route to the left it would be a perfect complement to Black Cleft in every way.....

Longland's just doesn't do it! 

That section of cliff is becoming increasingly hard to access - lack of visitors has allowed the undergrowth to thrive. A couple of routes  round there are currently unclimbable due to the vegetation on the routes I keep meaning to go back and do some cleaning - made a start on Gamin a couple of years ago but I expect the little progress I made has been undone by new growth.

There's a surprisingly large number of Yin and Yang routes in the UK (in the UKC logbook).

Left Wall and Right Wall. I know there are routes between them but if you closed the book they would be together. One climbed by many aspiring hard climbers and the other,  you've made it into the hard club.

But they're not really Yin and Yang in style (i.e. more or less opposites), are they?

Could be seen as safe crack climbing the other bold face climbing (I know it follows cracks though)?

As a very small example (next to each other but virtual opposites in style: pleasant balance climbing, very fierce jamming): Slab Direct and Slab Crack at Harrison's.

Us and Them on the Ramp at Avon - whilst there are a lot of routes between Us and Them the only thing between us and them is the zero option at e5

Black and White (not in that order, though) was our best day on Cloggy - both brilliant routes, very contrasting styles!

If only there 50 routes between these 2...
 

Surely they don't come more yin and yang than Appointment with Death (E9 6c) and Route I (HS 4b)?

This is a bit tongue in cheek but...

Someone doing AwD might not realise that Route I is a route (rather than a path)

Someone doing Route I might not realise that AwD is a route

The Boulder and The Black Cleft are pretty different?!

jcm

It could be argued thar Appointment with Death is merely a bastard offshoot of Route One.......

Yes, totally: what a pity it isn't called the Black Boulder (Or Boldest).