In Order:
Red
Blue
Crystal
Ruby
Leaf Green
Diamond
Pearl
Emerald
Heart Gold
I have completed the National Pokedex in Heart Gold (There is enough room in the pokemon center boxes to have at least 1 of every pokemon (i.e. bulbasaur, ivysaur, venusaur, charmander, etc. in order), and the variations of the formes (Deoxys (4), Burmy/Wormadon (grass, city, cave), Shellos/Gastrodon (East/West), Rotoms, Giratina (other/origin), Unown (all 28), etc.), a 6 pokemon team in the party and have 4 spaces to spare in the boxes.
I'm getting Pokemon Black first. I always try to get them in color order (RBY, GSC, RSE, FRLG, DPPl, HGSS), though I wasn't always successful (I didn't get Gold because I didn't have money, I got Leaf Green used, but would have gotten fire red if they had it. Now that I have money and my brother said he's going to buy my a 3DS, I'm more than likely going to get Pokemon White somewhere down the line.