I can't tell you specifically, because it will be quite zone-dependent. But a place you can get some good info is here:

http://www.carlsonsgardens.com/cal_color_frame_all.htm

Click in the left navigation area for different color groups. There are also tons of photos at this site.

Keep in mind that this calendar is for north of NYC (probably zone 6, though I don't know that for sure). So your bloom time will be earlier. But if you find something that interests you, you can ask around (at the Azalea/Rhodie forum, or nurseries near you, or Bob at Carlson's Gardens) about bloom time in your zone.

Hope that helps some!

I'd suggest stopping by a local nursery and see what they recommend for your area that stays that small. They might have recommendations besides rhodies and azaleas too since full sun in zone 8 might be a little tough on them. (Garden Centers often employ people without any plant knowledge so go with a long established nursery.) Good luck!

George Schenk suggests Mollis azaleas, narcissus, and heucheras around dogwoods. Living in the land of rhodies, you shouldn't have a problem going to nurseries around the bloom time of the dogwood and see what you like. If you live by Federal Way, there is the Rhododendron Species Botanical Garden to check out. They also happen to have a sale on Sept. 18, 9am to 3pm. I've been before, lots of knowledgeful vendors.

I'd second the suggestion to visit local garden centers or the Rhododendron Species Foundation Garden in Federal Way when your dogwood is bloom. The choices are nearly endless for rhodies and azaleas blooming in mid-April to mid-May in our area and you will be able to see and select by flower color and size what may work best for you. I'd encourage you to consider some of the lesser known and much lesser used species rhodies, many of which are smaller and later season bloomers and offer a distinctly different look than the more common hybrids. Of course later flowering rhodies are not a bad idea, either - it may be nice to have some later flower color after the dogwood is finished.

The Satsuki hybrid azalea 'Flame Creeper' is very attractive and offers coral red flowers in mid to late May. Good height for your lower selections.

And FWIW, Euonymus japonicus 'Microphylla' (boxleaf euonymus) will tolerate quite low light levels very well, but of course offers no particular flowering feature. The variegated form is much more attractive or you could try Lonicera nitida 'Lemon Beauty' for a bright splash of foliar color.

How about the Mucronulatum azalea,They are early bloomers.then you could try someting from the EXBURYHYBRID. Maybe you could think about pieris or even Mahonia . Perhaps I am swaying away from the tread oh well And lastbut not least drtdgr has the right idea about going to the nusrey N.N