Just wrote this the other day for my own board. Might as well copy and paste it here. 
Heated grips and heated gear will make winter riding enjoyable. I don't care how many layers of clothing and gear you wear, you will NOT be completely comfortable when the temps drop REALLY low without heated gear...
There was a great article I read somewhere that explained it best. I'll paraphrase...
Imagine the heat in your body is like a battery. The more layers of clothing you wear, the less DRAIN on that battery you're creating. However, you're never actually putting a charge BACK IN...
In other words, no matter WHAT you wear, if it's cold out you WILL get cold eventually without heated gear. The more you wear, the longer it takes, that's all... Saying it's better just to bundle up in cold weather is ridiculous. For one, you end up getting all bulky so you'll be less comfortable on the bike. It'll be more difficult to ride around. You're probably going to wear a lot of clothing under your riding gear, which will make the gear fit too tightly.
If you really want to ride year round, keep your body warm... I suggest you look at the following gear:
Gerbing heated jacket and pants...
http://www.gerbing.com
Variable heat controller for the gear... You can either use Gerbing's, or Heat-Troller's. I've used the Heat-Troller, but the Gerbing should work the same.
http://www.heat-troller.com
Now, you'll definitely want to keep your hands warm, too. You can use heated gloves or heated grips. A lot of people like gloves because that way the tops of your hands will stay warm, too... However, I prefer grips, since if you're going out for a short trip and you don't want to plug in all your heated gear you can still keep your hands warm... You can use Dual-Star heaters (thin, go under ANY grip of your choice) or HotGrips.
http://www.dual-star.com
http://www.hotgrips.com
Don't forget your feet! Heated socks will keep those toes toasty... If you want to go the budget route, look at
http://www.gorix.co.uk/acatalog/
click commercial/manufacturing
Gorix fabric is awesome stuff. You can order sample 3x6 strips off their site at the link I provided. Put the fabric in your riding boots. MAKE CERTAIN you put felt or some sort or fabric over top of it so you don't wear through the stuff. Also, make sure you have the fabric on a variable heat controller. That stuff will get BLAZING hot if you put 12v into it continuously!
Now, there is another option for the heated gear itself, too. Widder is another manufacturer. I don't like their stuff as much though it works equally well. They have a vest, arm chaps, and leg chaps that are heated. I just prefer a simple jacket and pants...
http://www.widder.com
If you don't want to go all out and get it ALL, start with heated grips. Warm hands makes a HUGE difference...
Heated grips and heated gear will make winter riding enjoyable. I don't care how many layers of clothing and gear you wear, you will NOT be completely comfortable when the temps drop REALLY low without heated gear...
There was a great article I read somewhere that explained it best. I'll paraphrase...
Imagine the heat in your body is like a battery. The more layers of clothing you wear, the less DRAIN on that battery you're creating. However, you're never actually putting a charge BACK IN...
In other words, no matter WHAT you wear, if it's cold out you WILL get cold eventually without heated gear. The more you wear, the longer it takes, that's all... Saying it's better just to bundle up in cold weather is ridiculous. For one, you end up getting all bulky so you'll be less comfortable on the bike. It'll be more difficult to ride around. You're probably going to wear a lot of clothing under your riding gear, which will make the gear fit too tightly.
If you really want to ride year round, keep your body warm... I suggest you look at the following gear:
Gerbing heated jacket and pants...
http://www.gerbing.com
Variable heat controller for the gear... You can either use Gerbing's, or Heat-Troller's. I've used the Heat-Troller, but the Gerbing should work the same.
http://www.heat-troller.com
Now, you'll definitely want to keep your hands warm, too. You can use heated gloves or heated grips. A lot of people like gloves because that way the tops of your hands will stay warm, too... However, I prefer grips, since if you're going out for a short trip and you don't want to plug in all your heated gear you can still keep your hands warm... You can use Dual-Star heaters (thin, go under ANY grip of your choice) or HotGrips.
http://www.dual-star.com
http://www.hotgrips.com
Don't forget your feet! Heated socks will keep those toes toasty... If you want to go the budget route, look at
http://www.gorix.co.uk/acatalog/
click commercial/manufacturing
Gorix fabric is awesome stuff. You can order sample 3x6 strips off their site at the link I provided. Put the fabric in your riding boots. MAKE CERTAIN you put felt or some sort or fabric over top of it so you don't wear through the stuff. Also, make sure you have the fabric on a variable heat controller. That stuff will get BLAZING hot if you put 12v into it continuously!
Now, there is another option for the heated gear itself, too. Widder is another manufacturer. I don't like their stuff as much though it works equally well. They have a vest, arm chaps, and leg chaps that are heated. I just prefer a simple jacket and pants...
http://www.widder.com
If you don't want to go all out and get it ALL, start with heated grips. Warm hands makes a HUGE difference...
