The only Pokedex I have attempted to complete without cheats is my Pokedex in Emerald since I do not currently have any games more recently then Gen III. I currently have 170/200 of the Hoenn Pokedex, if you do not include legendaries that are unavailable without the help of cheating. I have to trade with myself to gain the remaining entries (Pokemon that evolve when traded, the other starters, and Pokemon unavailable in Emerald)which I do not currently have the means to do but I should be able to soon.
I did complete the Pokedex completely on Platinum before I lost it but I cheated to complete it after I had captured roughly 75% of the Pokemans. Trying to catch them old eventually gets a little tiring.