i keep guppies with neons , black neons , glowlight tetras ,x-rays and (for all thoses people who told me not to)a male betta(amongst others)
i have never had any probs with them but a friend of mine had probs keeping some of the lager tetras with guppies(black widows, buenios airies and zebra danios)
in th end he gave his guppies to me.