ONE lens to rule them all

Finally looking to break into the DSLR game and probably going to do so with the new 600D. I'd like to start out with ONE lens... and will add to my collection later (maybe pick up a prime or two). We're traveling for two weeks this summer and kids are probably coming after that, so want good IQ but don't want size or weight issues.

(Size and weight... portability...this is why I'm in to the 600D, and not the 60D or the Nikon D7000... I'm hoping to be able to shoot video with it as well - to be honest if the Nikon D3100 had an external mic input like the 600D, I'd have bought it already)

I'm willing to spend some $ on a decent piece of glass, so I'd like some recommendations, but hoping to keep it to one lens.

I have played with the new Tamron 18-270 PZD and from the reviews here and elsewhere, think it is the one. All of Canon's standard EF-S glass have the DC micromotors, and to be honest are kind of loud and obnoxious (not to mention larger than the 18-270). The only exception IMO is the EF-S 15-85mm.

What are your thoughts! I much appreciate it.