It does depend on the temperatures you ride in, but layers are good, since you will find that you get very warm and sweaty as you warm up, even on a cooler day. Multiple thin layers are much more effective than one thick layer. Thin layers trap air, which warms you up. A good rule of thumb is always to start out a ride *slightly* cool (unless the weather is warm, of course!) If you start out in cool/cold weather warm, you'll overheat rapidly, but if you can put up with a couple of chilly miles early on, you'll be much more comfortable later, and not have a lot of extra clothes to carry along with you.
Bike jerseys are nice because they have front zippers for ventilation as you warm up and pockets in back to carry stuff (snack, bandanna to blow nose, whatever...) They also tend to be rather form fitting, which is good on a bike. Don't need lots of extra flapping fabric acting like a sail. They are also typically constructed of quick-drying, wicking fabric, good for sweat!
As far as brands, I find Shebeest, Terry, and Pearl Izumi to be flattering for a woman's shape and come in cute styles and colors. Jerseys are definitely not unisex, and most men's jerseys are too long and not cut right for women's bodies. The elastic at the bottom rides up on our hips. Our forum sponsor here, Team Estrogen, is an excellent place to purchase great women's gear -- and they have good sales too!
But, wear what you like. There is certainly no rule that says you must wear jerseys. On my mtb I don't need the rear pockets since I use a camelbak, so sometimes wear wicking fitness tops (for runners, gym, etc.), and those work fine too.
Last edited by emily_in_nc; 03-01-2009 at 04:41 PM.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow