I never ever used to name my Pokemon, but now I'm obsessed with nicknames! They have to have them, even if they're the dumbest most boring names you can imagine.
I haven't played through any Gen IV games in quite a while (though I want to do Diamond Version really soon), where I'll definitely pick Piplup and perhaps name it... Sashimi? I named my Samurott that in Gen V and loved it, it goes excellent with most Water-types cx
In HGSS I always pick Chikorita, and I almost always end up nicknaming it the stereotypical Sakura, which is perfect for Meganium!