You may or may not be aware – however there is a list – in fact I think technically speaking there are two lists*. In terms of North Wales cycling climbs within the top 100 you have plenty to choose from.
The nice people at have compiled a list of 100 Greatest Climbs, and Another 100 Greatest Cycling Climbs.
For thoseĀ  who want to narrow this noise down a little to a tick list – Britain’s Top 10 Toughest Cycle Climbs from the Guardian – Hardknott and Wrynose old news to those on the Fred Whitton Challenge, and Bwlch y Groes from such wonders as the Bala Devil and the Wild Wales Challenge events.
Now – it is unlikely to have escaped your attention, that living where we do that we have a lot of hills here. It is not really a surprise given that we are based on the end of the Clywdian Range, and being not all that far from the Snowdonia National Park. Going uphill is not something that is easily avoided.
So here is a list of the locals of note – you may wish to look them up on Strava, or maybe even go hunt them out:

Top 100

#86. The Shelf – 262m – 5 to 15% – 5.1km
#87. Moel Arthur – 220m – 10 to 20% – 2.2km
#88. Penbarra (Bwlch Pen barras / Bwlch Penbarras / Old Bwlch) – 258m – 11 to 25% – 2.3km
#89. The Road to Hell – 353m – 3 to 20% – 11km
#90. Horshoe Pass (Bwlch yr Oernant) – 317m – 7 to 20% – 6.1km
#91. Bwlch y Groes (Hellfire Pass)- 385m – 11 to 25% – 3.5km

Another 100

#188. Melin Y Wig – 100m – 1.3km – 8%
#189. Llanberis Pass – 247m – 4.9km – 5%