Never owned any uncut sheet or saw any irl. The ones I have seen online can also all be found in the link that @azulryu provided.
One I especially like are the Skyridge Box Toppers, which contain both German and Italian ones on a single uncut sheet:
I know that almost all European cards (for both Pokémon and Yu-Gi-Oh) are printed in Belgium, but it’s cool to see a single sheet with two languages like this.
I also really like the 20th Anniversary sheets that are (or were?) hanging in the US Pokémon headquarters in Bellevue WA (sources: this thread I posted back in August 2017, and this reddit post):
The cards used are all over the place, even including WotC era cards. There are also some English/Japanese backs and Unown mixed in randomly. Of course they don’t really give any information about the history of Pokémon and how they produced them, but I still like them for how random and unique they are.
And another one I of course like for obvious reasons is this Japanese Pokémon Best Song Collection CD sheet for the Pikachu. This is one sheet I wouldn’t mind owning in my Pikachu collection. 
I’ve also showed some uncut sheets in my picture dump thread, but I think all of those are also mentioned on that website Devin linked.
Greetz,
Quuador