i think it will be easier for the pros to answer your question if you provide a bit more info about your situation.
what size tank, equipment, etc
im assuming you already have a guppy and thats why you dont want anything aggressive? if you dont have any and your wondering what fish will work well together in a community tank you should have a look thru some old posts, aswell check out the articles section.
i dont know any specifics but i do know a general rule would be similar sized fish get along well. guppies are small, you probably dont want to get anything that will grow big, i would have a look at what fish are available in your price range and then look them up individually on wikipedia, or post another question once you have some ideas.
i am 100% not sure about anything to do with fish, just trying to help you along in the right direction.
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