Cold weather in Israel can be considered 'freezing cold' if the temperatures plummet below 10-15 C. On a trip to Cyprus during December virtually everyone was wearing thick down jackets and some were even wearing hats and gloves and most were complaining about the freezing weather conditions during the evening. The temperature must only have been around 13-15C. I was wearing a short sleeve cotton shirt and thinking what a nice evening it was after the heat of the day (about 21 C), which would have been considered a warm Scottish summers day.

So I guess you'll probably need a warm sleeping bag if it is to be used for winter conditions and will probably need to be rated down to at least -10 C if used in local winter desert conditions.

Being a resonably dry part of the world a down bag would probably be fine for your purposes being very lightweight but slightly expensive. Down bags can be up to half the weight of even the best synthetic bags. Generally the better quality down, the lighter the sleeping bag and the more expensive.

There are lots and lots of high quality manufacturers.

PHDesigns - http://www.phdesigns.co.uk
Alpkit - http://www.alpkit.com/shop/cart.php?target=product&product_id=16244&category_id=253
or a slighly more cost effective bag from Alpkit
http://www.alpkit.com/shop/cart.php?target=product&product_id=16321&category_id=253

Marmot - http://marmot.com/fall_2008/equipment/sleeping_bags
Rab - http://www.rab.uk.com/products_sleeping.html
Western Moutaineering - http://www.westernmountaineering.com/index.cfm?section=Products&page=Sleeping%20Bags
Mountain Hardware - http://www.mountainhardwear.com/en-EU/Category.aspx?top=1561&cat=1561&level=1

For Synthetic bags

Snugpak - http://www.snugpak.com/index.php?MenuID=160-101
Wiggys - http://wiggys.com/category.cfm?category=6

There are still lots of good manufacturers not mentioned here.