I wrote and produced the following with NESTri, NESPulse and NESNoise:
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You can find those VST plugins and plenty more here:
http://woolyss.com/chipmusic-plugins.php?s=NESTri+-+NESPulse+-+NESNoiseWhen you say "Pokémon" the GameBoy comes to mind, so it's certainly that NES\Famicom synth type of sound. But the original hardware has a very limited amount of simultaneous channels (4 channels maximum or something like that).
Modern "chiptune" or "lo-fi" music pieces use these chiptune sounds without the shortcomings, so you can pair them with modern effects such as reverb, compression, delay and sampled instruments.
Example:
(track by Carlo Castellano).
You may also find interesting the effects of "bit-crushing," using a plugin to deliberately add resampling noise to your sounds to get a "lo-fi" character:
http://www.gamedev.net/topic/628838-how-to-get-lo-fi-tones-and-sounds/