Need help deciding between two telephoto zoom lens options

[jennT1i]

I purchased my first dslr, a Canon T1i, a couple of months ago.  I opted out of the kit lens and purchased the 50mm f/1.8 instead.  I purchased the dslr to take better pictures while traveling, which also means I can't carry around too many lens while on the go.  I am looking for 2-3 lens that cover most of what I'll need while traveling.  I'd like to stay under $1000 for each lens, at least until I get better.

I've decided on the EF 17-55mm f/2.8 IS USM but can't decide between two telephoto options.  Am debating between:

A. EF 70-200mm f/4 L USM
B. EF 70-300mm f/4-5.6 IS USM

The price is similar between these two, so I guess the question is whether to choose the "L" series or the IS?  Which is more important?  What would you recommend?

[KeithB]

If you are hand-holding, IS by a large margin.  I really like my 70-300 IS.  You might also want to think about the new EF-S 15-85, probably smaller and lighter and plugs up the "hole" at 55 - 70 mm.

[Bob Atkins]

My choice would be (and is) the EF 70-300/4-5.6IS USM I've owned and used both lenses. While there is no doubt that the EF 70-200/4L is a very fine lens indeed (and can take the Canon 1.4x and 2x TCs), I simply find the EF70-300/4-5.6IS USM more useful because it (a) has a longer reach and (b) is image stabilized and (c) it's slightly smaller and lighter. The IS is a very big plus with a telephoto lens. The image quality of the 70-300 is very good, desite it not being an "L" lens. On a recent trip to the UK I found it was the lens that I used most.

[whizkid]

I have both a 17-55 and the 70-300.  I agree with the 70-300 as a lens for travel for the reasons Bob gave. I don't think of the 17-55 as a travel lens. I would second getting the new 15-85 and a 70-300. 

[jennT1i]

why would the 17-55 not be considered a travel lense?  why would the 15-85 be considered instead? 

[whizkid]

For travel I like something with greater telephoto reach than a 17-55 lens offers.  A lot of travel images are grab shots and the less time spent changing lenses the better. If you use a lens like the 15-85  it would probably be all you need except for an occassional 300 mm shot using a 70-300 lens. The 17-55 is a great lens but it's a lens to use when a larger aperture is more important. Given the great job that Canon's cameras do at high ISO I don't see such a need for travel shooting. For travel I would rather see size and weight of a lens be about greater zoom versatility than a constant fast aperture.