Pokemon Indigo is a good website to play on. You can easily get almost any Pokemon at any level and items as well.
http://www.pokemonindigo.com/
You can no longer play Pokemon Crater. The creator of the site has shut it down on December of 2007.
I don't think that there is a current site that you can play Pokemon Yellow on, at least not legally.
Proxy site or other method of tunnel site.
Pokemon Showdown, take a look over at Smogon.com
Yes, very, all it is is a site to play Pokemon on, they are perfectly safe
You can get the Japanese Pokemon Black & White in some shops in Japan, or you can pre-order Pokemon Black & White on a site called Play Asia.
What are you talking about? Pokemon games are played in Nintendo DS' or Nintendo DSi and Nintendo DSi XL. The games avalible are Pokemon Heartgold, Pokemon Soulsilver, Pokemon Pearl, and Pokemon Dimond, these games are played on the Nintendo DSi, DS, and Nintendo DSi XL. You can also play games online, Play on the official site, Pokemon.com.
The site called Playr allows you to play all the Pokemon games (or at least several) for free, you can even save!
download the gameboy emulator and then find a site with roms and choose Pokemon sapphire.
if you want to play pokemon online they have a few on playr.org ex: pokemon crystal, pokemon soul silver and heartgold are on that site they are all old games theres also pokemon yellow, pokemon red, pokemon blue and pokemon green.On PlayR.Org
for me the best site is Pokemon lake but if that gets boring then try Pokemon indigo or Pokemon volcano
use a proxy server/proxy site just search proxy on google