backpack recommendations

You are in luck: this subject has been discussed many, many times on this website, and you can retrieve these discussions by using the search box in the upper right corner of the webpage.

I would say break your needs down into two groups.

1 - What you need for 4 months in Israel.
2 - What you need for a 3 week jaunt around Europe.

At the end of the 4 months ship home anything you don't need for the 3 week jaunt.

As for bags Rick Steves Convertible Carry-On bag is supposed to be a good bag. I just ordered one from REI-Outlet for about $75 shipped. It is last years model on closeout.

http://www.rei.com/REI-Outlet/product/759517

I have both Rick's Convertible/backpack/carry on bag and his Roller bag. The convertible bag is not intended to be a heavy-duty backpack such as the kind you would want if you were doing hiking or long distance street walking with it strapped on your back; it is really good for shorter periods of walking in situations like stairs or long lengths of uneven surfaces where a roller bag would be a problem. But for train stations, airports, and hauling on even surfaces such as sidewalks, many prefer the roller style bag. Each style has its fans, as I said, I have both.

I like Northface Bags, and Mountain Hardwear has some great new ones. But overall - you need to get what feels right so go try some on at your local sport store such as REI or any big hiking chanin. Make sure the staff actually goes hiking and ask them the pros/cons of various models. They will ask you the same others did here - what you want to do, how much stuff etc.

Try Eagle creek. They have very good reviews. I just purchased one from REI.com for $75, a last year model. 2007 one is about $200.
It's only 2.5 lbs and it has a day packpack and it's convertible .
I used to have a backpack from national geopraphic also with a daypack. It was pretty roomy, 23 in long, but the problem I had with this packpack was the zipper was catching the over-zip fabric when I was zipping it... I was able to fix it every time, but I thought it was unconvenient.
I can't wait for my new packpack.
Ebags.com has a nice web site set up, they post pictures of each item and description and reviews. maybe it help to get an idea.

I found a bag online from Ebags that was similar to Rick's convertable carry on but a few more features and half price. It worked well for me.

My wife insists on rollers for her bag, she and the kids all used regular roll-on carry ons.