Well, since the all-might Kaijumaster, and my second in Pokemon fandom, has invoked the name of Pikachu, I must put forth my two cents. I am one of few who has picked up pokemon and NEVER put it down. I have EVERY version in every series, though console titles post-dating Stadium 2 have never been purchased. I reinforce Trevor's support of Snap, since Stadium erased out games

Poop on you stadium (except your mini-games). Anyway, yes, you've missed ten years of good clean gaming fun.
As several others suggest (and I remarked in another thread), at this point in time the best place to go is Fire Red/Leaf Green for the GBA. Remakes of the originals with all the menu and graphical improvements fans were dying for. They have a reasonable playing time of 30-40 hours, so the month before DP is plenty of time. Also, the GBA ones are compatible with the DS ones, so your efforts are transferrable to the newest games :thumbs:
Several others also mentioned Gold/Silver/Crystal. I like to call this the forgotten generation. Many people abandoned the franchise at this point, and the young whipper-snappers who came in afterwards do not appreciate it *slaps* It brought forth day and night, breeding, and a host of other features that remain key in the current games. If you get a chance, try one out for the GBC, and join the rest of us in PRAYING that they bring the region, Johto, from those games back (there are actually hints of it in DP, though it is not accessible). It actually is the only game to include two full regions to explore, including the original Kanto, and it kicks the ass of lame old Hoenn from Gen-3. Man that map is such a pain to travel on...
Anyways, I do not wish to usurp your leadership, good sir, but I emplore you to pick up a copy of this wonderfully fun series ^_^ I appreciate Trevor's appointment of myself as the Poke-sage here at HJU, though there are more skilled than I out there - I am just a knowledge bank and force of enthusiasm for the franchise (ie - biggest fan in my respective state township).
My last words are thos of warning - don't become uber-obsessed with the in-depth technicalities of the game, which you undoubtedly discover. It happens to so many, and at one point almost drove me from the franchise. The key to this game has always been keeping it fun - so go grab a copy of FRLG (they;re only $20 new) and start an adventure!!
Pokemon, GETTO DA ZE!!!