More and more brides are starting to realize that it's just not feasible to make their bridesmaids/attendants wear exactly the same thing and pay hundreds of dollars for a dress that will sit in the back of their closet, never to be worn again.
The solution? Pick a color scheme and have your bridesmaids buy a dress that they like that fits that color range. It could be all shades of one particular color, or colors in the same family (jewel tones, reds and pinks, greens and blues). One of the first brides I ever worked with did this and I think it turned out perfectly (see below)! What's even better is that each of the girls can wear their dress again.
The other hot trend right now is patterned bridesmaids dresses. These may not be as practical or cost-effective as just going with a color scheme, since they would most likely need to be bought as a set. However, if you have your heart set on matching bridesmaid dresses, a flattering pattern for all is a fresh and interesting approach.
If the vibe of your wedding is much more casual, you could even combine the two and have a color range, but lots of different patterns and styles.
IMPORTANT: if you want to play with colors, patterns, or dress length, at least one should remain a constant. The picture below is a perfect example: the dress length is the constant, while the patterns and colors vary (even though they stay in the blue family).