If you’re serious about wahs, look into a Teese wah at http://www.realmccoycustom.com/
This guy is reknown as a retro wah king. I have one of his (Picture wah) and love it but I also switch his and a Vox 847. I had it modified and it just sounds cleaner for my amp. I love the Teese for Clapton-esque overdrive tones but I like to engage the wah when I play clean and the Vox just works for me. Both are great really.
Damn, those are pricey, but the RMC3FL looks amazing. It will definitely be in the running when I finally decide to splurge and get a decent one. Thankya!
I haven’t clicked on the link but have heard the story. Having to stay sync’d up with your foot on the wah and playing that lick for hours is really, really hard to do. What was the story about James Brown’s guitarist, Jimmy “Chank” Nolen (say “chank” out loud in a funk groove and you’ll understand the nickname). I think James Brown turned to him at his audition and said “Can you play an E9?.” “Yes, Mr. Brown.” “Can you play it for 45 minutes?” 
Made me think of Massive Attack’s Protection (1994). Actually, looking into it a little further, it’s a sample from The Payback by James Brown so it’s not ‘real’ but anyway, it’s a nice touch.
Also, The Temptations’ Papa Was A Rolling Stone. Courtesy of WahWah Watson
I’ve tried wah, and been unhappy with it. It just sounds forced and artificial when I try it. Also the coordination of playing with three limbs is distracting as hell, and it’s very hard to resist foot-tapping the beat on the wah, which doesn’t give good results IMO.
Here you go, OP. Scroll down and click on the link for “Instrumental: The Wah Wah Pedal.” Plenty of examples of great use of the wah, as well as the history (originating from the “wah” sound of muted horns). (And timely, too! That show just aired two months ago.)
Watch it anyway; it’s cool just to hear him tell it.
Oh! I missed the request for examples of it being used effectively. The sound that comes to mind when I think wah pedal these days is Otoko. Katz Kobayashi is coming to you in your left ear. He’s playing pedal steel and working both a wah and volume pedal, plus three pedal steel pedals that control the pitch of combinations of strings. Your right ear gets Susumu Oku, who alternates between lush and screaming on a regular six string guitar.
For the combination of low price, simplicity, and tone, I personally like the **Morley Bad Horsie 2 **endorsed by Steve Vai. There is no on/off switch. Just start pumping the wah and it automatically turns on the effect. The main downside, if any, is the pedal requires foot contact to be ‘on’ and cannot be locked into a static tone (i.e. not oscillating) with foot removed which is important to some guitarists. The Bad Horsie 1 is basically the same except without the flexibility of the tone contour knob.
The Boss Auto Wah AW-2 is good those who want constant rate oscillating wah wah effect without foot contact. The price is at the low end. Tone is good but not optimal to my ear.
Landgraff Wah is a great boutique pedal if you can find one and have a large budget.
Volume/wah combination pedals exist, but I do not personally have experience with these. Search for the Morley MWV, Donner Wah Cry 2, and Hotone Soul Press 3 in 1 as examples.
I have not used any of the RMC wah pedals but am intrigued.
I can think of a few…
“White Room” by Cream (Eric Clapton rocks the wah in intro chords, chorus rhythm, lead guitar licks in 2nd & 3rd verses, & outro lead solo)
“Tales of Brave Ulysses” by Cream (heavy wah in riffs and rhythm guitar)
“Still Raining, Still Dreaming” by Jimi Hendrix Experience (main riff whole song has wah-wah effect)
“Burning of the Midnight Lamp” by Jimi Hendrix Experience (intro & rhythm)
“Voodoo Chile (Slight Return)” by Jimi Hendrix Experience (intro riff)
“All Along the Watchtower” a Bob Dylan tune as performed by Jimi Hendrix Experience (part of the middle guitar solo starting at 2:16)
“Car Wash” by Rose Royce (funky bass wah)
“Tell Me Something Good” by Rufus & Chaka Khan (funk rhythm)
“I’m the Slime” by Frank Zappa (wah-wah in guitar intro and outro)
“Flower Punk” by Frank Zappa & The Mothers of Invention (guitar rhythm)
“Corporal Clegg” by Pink Floyd (rhythm guitar during chorus starting about 1:02)
“Money” by Pink Floyd (electric piano with wah wah…kind of subtle)
“Electric Funeral” by Black Sabbath (fuzzy wah-wah)
“Beauty Lies in the Eye” by Sonic Youth (rhythm drenched in distorted wah-wah)
“Diamond Sea” by Sonic Youth (this sounds like an Auto Wah to my ear)
“Home” by Dream Theater (part of the intro beginning 1:44 and again later in the song)
“blood sugar sex magik” by the Red Hot Chili Peppers (mostly during the verse and interlude)
“All I Really Want” by Alanis Morissette (rhythm guitar)
I would need to do some digging to find more recent examples.
Wow, you know your wahs 
- How would you assess the state of wah use in music today?
- what do you think of Kirk Hammett’s use?
- Do you agree that it takes investment of time to get the wah integrated into your technique, or does it just come rhythmically?
-I occasionally encounter the wah-wah sound in newer music (2010 to present day) while at music festivals or browsing music on the Bandcamp website. The music industry is so fragmented today and much more recordings are being released each week compared to previous decades, so it’s really difficult to ‘assess the state of wah use’.
-I have not listened to Metallica in the past 20 years aside from the occasional ‘Enter Sandman’ blasting from the speakers of a vehicle with windows rolled down. I do not have enough study in this area to form an opinion.
-It really depends on how the wah-wah pedal is used. Some techniques are easy and some are not. Sometimes the use of wah-wah is rhythmic but sometimes it is static or dynamic.
My example with Amplitube simulated wah…just listen to the beginning and the end. One of my first home recordings, Be gentle.
Here’s me (45 seconds in) using the EHX Crying Tone, which has a warmer tone than others I’ve played - and no moving parts!
Link to EHX page too.
MiM
Lots of folks tried to use a wah pedal. Clapton and Zappa used one for lead guitar very well. Jorma Kaukonen used one a bit more subtly, perhaps more as a tone booster. I used mine more as a tone booster. A lot of people used one when playing their guitar as a rhythm instrument (Theme From Shaft).
Hah, now I know why you dig Royal Blood doing My Sharona but not their heavier stuff. 80’s dance pop - fun and it sounds like a good cause. With a wah rhythm and everything!