jimmmmmo: nothing for PC that i know of, but for DS/3DS is Alpha Saphire (which i highly recommend) and you can get the orignial red/blue/yellow on the nintendo online store, which will always be the best in the series :D
Gede: So, for someone who never played a Pokémon game, where should they start? The old ones? I never understood what changes from red to blue to other colours.
Start with the newer ones. There are so many quality of life improvements that later generations have it's extremely difficult to play the old ones.
Plus, used Pokemon games cost almost as much as current ones, you can't really save money by buying used.
Alpha Sapphire / Omega Ruby or X / Y are out now. Moon / Sun are just coming out later this year, so that might be nice as a present. If you do go for an older game I wouldn't go any older than Black / White.
Pokemon games come in 'generations'. EX, Red/Blue/Yellow are one generation. Generations take place in the same region, with basically the same story, just slightly different pokemon available. Different generations take place in different regions and have different stories, although there are never really any drastic changes. Later generations are genuinely better in things like gameplay, user experience, interface, etc. Lots of people are diehard fans of the first game they played, but honestly a modern gamer is better off trying the newer games as their first experience.