Here are some of my favorite bridesmaid dress collections...
http://www.edenbridals.com/
Eden has super cute bridesmaids and a wide variety of colors. Most don't have sleeves, but would look very nice with a bolero or cardigan.
http://www.venusbridal.com/
More cute bridesmaids, lots of colors. They also have a modest line (called "Temple Maids").
http://www.mikarose.com/
These dresses are less formal - more like Sunday dresses - but because of that, they are also inexpensive. The color selection is limited, but they can be ordered (or purchased in some areas) very quickly.
http://www.barijay.com/
Love, love, love this collection!