"All" pokemon - how many games?

Playing through Heart Gold at the moment and wondering, if you wanna catch all pokemons (I know some you need event for) how many games minimum you need to play?
A list of the games would be awesome :-P.

There's no specific minimum amount of games you need to catch them all. Back in Red and Blue you you just had a few Pokemon ypu couldn't obtain on one game so you could just ask a friend to trade you them. Nowadays there are 649 (and counting) Pokemon in the franchise meaning it's a bit harder but more entertaining. But seeing as you're in HeartGold you'll need 493 to catch them all. Now a good chunk of Johto and Kanto Pokemon can be caught in your game, but you'll have to ask someone to trade you any Pokemon exclusive to SoulSilver. HG gives ypu a nice few Hoenn/Sinnoh Pokemon too but in this case it's probably a good idea to have one or two Gen 3 games (I reccomend Emerald and either FireRed or LeafGreen) and another Gen 4 game (I reccomend Platinum) and then you'll almost have them all so probably ask someone to do a Gen 4 trade with you for the rest. :)

What i mean is, if i want to catch all released pokemon so far which games should i play?

If you wanna get technical about it, you'd need Black, White, Heartgold, Soulsilver, Sapphire, and Ruby. In all honesty it's dumb to get all those games though when you can just trade with somebody to get the Pokemon that your game lacks. An easy way to fill your pokedex is to post a trade on the actual GTS, for example, post a Mareep for a Tentacool, and I guarantee you'll get the Tentacool within a few days because you didn't request a level 1 legendary. Just post reasonable trades and you'll get them!

Hey Fletch, you're forgetting a region.

And Isbiten, from someone who has completed the National Dex and has a living dex, try to get as many games as you can if you want to avoid trading over the GTS (which is completely convoluted). Having bought at least one of every "paired game" it was easy to just migrate up. By the time I migrated everything to my Black save file, all I had to do was catch the Unova pokemon.

heartgold/soulsilver platinum and black/white