When I read about abduction cases, I always see them talking about little grey aliens. I was wondering if there is any info on different types of species. And which type are hostile and which are peaceful.

Do a google search for extraterrestrials.

Size is such a relative term, so they may not be small. In their race they may be considered big, but to the humans they are small. So if you want good information dont use small, large, tall, big, use messuerments.

Simon has a list of different ones on the main ATS site (under extraterrestials)

according to a pretty good cross-section of UFO folklore, there's at least as many as 9 different species, that seem to be the most prevalent, with a sprinkling of others. Seems we're becoming a popular intergalactic tourist spot....

The most intriguing to me, is that there are lots of independent sources linking the greys to the yellows (which resemble the greys, only slighter, taller, and the yellows seem to be in some kind of "master" role to them).