I'm not sure which one was the overall first, but I think Nidoran(female) was the first Pokemon I saw in one of the games, Lapras was the first one I saw in the anime, and Dugtrio (and later Vapereon) for the "other" category. As for the first one I ever saw on a card, it may have been Machamp, but I dunno.
The first Pokémon I have ever seen is Pikachu! 
I've seen him in the television. (For I do not have GBA at that time. 
)
I kept seeing Pokemon commercials with Pikachu so yeah, Pikachu.
First one I saw as a Charmander during one of the first episodes of the anime I saw.
I remember when I was about 6, I got Pokemon Red, and when you went to pick a Pokemon, I happened to click on Squirtle first.
I have to say mew that's when i heard of pokemon and when i was little people just said the pokemon mew no one else.^^
i think it was a treecko for me cause i only had ruby then
no w8 maybe it was bulbasaur
or was it suicune
Mine was..voltorb.I remember watching the first episode about three seconds or so in to it and I saw ash slep-battling and he was holding a voltord toy as a pokeball!