I like KillarneyRose's dress. The plum color is very nice.
What time of day is the wedding?
If it's during the day and maybe a little more casual, I would consider something like this from jcrew:
a cute little dress in the color petal:
http://jcrew.com/catalog/product.jht...94&catId=43830
a sweater in case it's cold, in oatmeal heather:
http://jcrew.com/catalog/product.jht...91&catId=44056
cute little shoes, in natural:
http://jcrew.com/catalog/product.jht...91&catId=44077
or, if it's cool, boots, also in natural:
http://jcrew.com/catalog/product.jht...orName=NATURAL
If it's more dressy, later in the day, I think this dress is nice (can you tell I like brownish/beige colors for fall?):
http://store.nordstrom.com/product/p...tyleID=2796740
Here's another nice one:
http://r1.east.rmi.yahoo.com/rmi/htt...ategory=200302