Hi Cosmo. That is indeed quite a tough restriction, but I'm determined to set you straight as this kind of lifestyle is important to me. It seems like you're just looking for an outsiders' perspective, not necessarily advice, but that is the format I ended up giving it in, heh.
I think wool and other animal-based fibers are more prominent in winter simply because they are warmer, and that is the only reason we associate them with fall/winter. I am of the belief that fabric should not be seasonal EXCEPT in a functional sense--so while many ladies here would faint at the idea of carrying a tweed bag in summer, I would totally do it as long as it goes with my outfit and serves its utilitarian purpose. I'm not "wearing" it, so there is really no reason the fabric should matter. I will say, however, that I am in the minority on this, so you might not want to listen to me.
So having said that, I can think of lots of things that are appropriate and dressy to me, but I can't say if they're seasonal or not because I don't really care about that :p. The fabrics might not be as warm, but they'll still serve you well, I think (and you can always put some long johns or something underneath if it's really freezing). I have a pair of velveteen trousers that are very dressy and definitely seem wintery to me. Cotton sateen would have a lovely sheen to it, and as long as it's in a darker color, I think it would look great.
http://www.jcrew.com/AST/Brows...../12591.jsp
http://www.bergdorfgoodman.com.....4cat211120 (those are the pants I have, too bad they don't fit)
And of course, regular old cotton is a year round option as far as I'm concerned. The only dilemma I have is that I like my pants to have a bit of drape to them and cotton can often be stiff and rigid.
I'm also interested to see how bamboo and hemp take off as alternative fabrics. Right now all I can seem to find are yoga pants, clearly trying to court the granola munching hippie demographic. If they really want to make a difference, they'll have to start marketing to the rest of us. Hopefully that will happen.
As for sweaters, I love just plain old boring cotton sweaters. They are warm enough for me in the winter, but light enough for me in the summer, they aren't scratchy like wool, and they don't pill or wear out as quickly. My basic black cardigan comes from the Gap and has lasted me 3 years now and still looks great.
I'm not positive but I think Angie has a wool allergy, so if I'm correct, she doesn't wear cashmere or wool either. When she is back she might have some input on this.
As for synthetic options, acrylic, rayon, and polyester are all options and they really can look beautiful depending on the design. Personally I don't care for acrylic because it pills too quickly, but it's fairly inexpensive and it can look just as nice as wool, if only for a short period of time. There is also always polyester and rayon. Some fashion snobs may scoff, but I'm pro poly and rayon as long as they look and feel good, and I think that is the YLF consensus. In fact, these pants are a poly-rayon blend and I think they look lovely.
http://www.espritshop.com/Shop.....01_001.jpg
I have some poly/rayon dress pants from Esprit myself and I love their drape.
Tweed is definitely a winter fabric, and it CAN be found in non-wool fabrications. This lovely jacket is a cotton "tweed":
http://www.bcbg.com/product/in.....age=family
I imagine that would be hard to find, but it would be such a great piece to have as someone who is both vegan AND style-conscious.
I think as long as you're not wearing linen or some kind of flimsy, cold-looking fabric, no one is going to notice or care. A sweater is a sweater after all. No matter what it's made out of, it will never be a summery garment!
