Small Tree Collection
Not a generic collection but one based on the fact that the trees are all of relatively small stature.  Most home landscapes have the need for small trees as well as shade trees.  Some of the best would include serviceberry (Amelanchier sp.) and Japanese tree lilac (Syringa reticulata).  A common small tree is the Amur maple (Acer ginnala).  It is very popular because of its rounded form, ease to prune, disease resistance and beautiful fall color.  There is one drawback and that is its massive production of seed and its ensuing invasiveness in many areas.  Use with caution!  All the crabapples and hawthorns are generally small stature trees as well.