If you are in an area with acid soil, low bush or half-high blueberries like Northblue or Northsky have white flowers and stunning red fall color in addition to the berries, and heaths and heathers have both evergreen (or colored) foliage and flowers. Rododendron 'Checkmate' has stayed around 3' for me for at least 5 years as has 'Yaku Prince'. 'Purple Gem' is another that stays low. Below I've given you the link to the American Rhododendron Society's data base search page, where you can put in a maximum height to search for others.

Some shrubs that are less fussy about soil:
-There are many low-growing spireas.
-Deutzia 'Chardonnay Pearl', 'Yuki Snowflake' and Nikko all stay short.
-There are low-growing Weigelas such as 'Fine Wine' and 'My Monet'.
-Cornus 'Arctic Fire' is supposed to stay below 4'.
-Caryopteris 'Sunshine Blue' has gold foliage and blue flowers in late summer - fall and grows well for me. There are other shorter Caryopteris that do well in zone 5, but not all will survive and some will die back to the ground and need once yearly pruning to a few inches.

Here's C. 'Sunshine Blue'

Here is a link that might be useful: American Rhododendron Society database search

This post was edited by nhbabs on Wed, Jul 24, 13 at 19:03

Spirea 'Golden Elf' is a great one--yellow foiliage and highly deer resistant.
(Cornus 'Arctic Fire' definitely gets to 4 feet--and requires yearly pruning to the ground to get the best winter color, but it's a nice cultivar since it doesn't sucker)

There are small cultivars of Rhodies and a couple of Pieris too.

I love Dwarf English boxwood (Buxus sempervirens 'Suffruticosa').

I have read hardy to Zone 6 on some sites, 5 on others. Deer will never eat them.