What comes to mind...

When you think about rare, non-legendary, pokemon? (Trying not to include DPP pokes yet or starters btw)

-Eevee
-Chansey
-Beldum
-Lapras

Those are what immediately come to mind. So, what about the rest of you?

Lavitar and Alakazam came to my mind first.

scyther
clefable <33333333333333
kengaskhan

Let's see:

- Eevee: Before D/P/Pt, it was always obtainable as a gift.
- Porygon: Because it was very expensive to buy.
- Kabuto and Omanyte: Back in the old days, you could only get one or the other unless you trade with somebody. Aerodactyl was lucky since you get the Old Amber as your second fossil.
- Hitmonlee and Hitmonchan: Exact same reason as Kabuto and Omanyte. You only can pick one of them in R/B/Y.

The thing that first came to mind for me was Absol :> I dunno why, though. Probably 'cause I've always wanted one, but I'm too lazy to actually get up and find one. 8D;

I automatically thought of Kangaskan and Tyranitar.

Pikachu was quite rare in veridian Forest in Red/Blue, I guess. :\ Funny how loads of people say Scyther, but dont say Pinser. :P

Absol, Scyther, Pinsir, Heracross, Chansey, Feebas, Relicanth and Clefairy.

I don't really count gift pokémon, since they're readily available.

Kabutops, Aerodactyl, Umbreon, Porygon, etc...
I think there's other of them but it's random to my mind xD

I always think of Eevee, I always looked forward to receiving one so I could decide which evolution path I'd choose for it. Normally it resulted in a Flareon for me.

Anorith, anyone? It's the last pokemon that would look "normal". Anorith has even made less anime appearances than Armaldo.

I also thought of Lapras and Spiritomb right away-

i automatically thought of tyranitar and ninetails, dunno why as ive never caught either of them :)

I automatically thought of Dratini, because i wanted one but always failed at the slots and didn't feel like forking up enough Poké to buy one.

Absol and Tyranitar come to mind.

Feebas and Chimecho are the first to come to mind.

*recalls the several weeks it took to acquire them in R/S*