Rules of Thumb for Polygon Counts?

I'm asking almost specifically for the unity3d asset store. I can't find this information in the guidelines. I've never created art for games in particular. So, I'm wondering if there are any ballpark figures for numbers of polygons to aim for in varying game objects?

For example:

Small building with interior spaces (say a big tent).

A small animated animal?

A human character (I gather this is around 6K polys?)

An airplane or similarly sized spaceship (not a giant fleet vessel)

Thanks for any tips!

Since Unity supports such a variety of devices, there is no set "rule of thumb" for polycounts on models. If you are making a full-fledged PC Game then you can probably go hog-wild and have models with 30K tris, however if you are supporting older iPhones, you can't really get away with much more than 1K models (assuming in both cases you have a reasonable number of on-screen objects.)

This question pretty much covers it:

I would say if you are planning to contribute to the assett store that it wouldn't be a bad idea to include a few different "tiers" of polycounts for your models that would allow devs to pick the version best suited for their project.

Also it's important that you include that info on the model.