I use the Tracks Compact Travel Staff monopod, with a Tracks camera extension. It is adjustable in height, sturdy enough to double as a walking stick in rough terrain, offers a terrain foot and a rubber foot (and a mud foot attachment), and folds to fit in a carry-on suitcase. It is not perfect (some heights are not achievable), but I have been happy with it. Tracks sells several models but this is the only one that fits in a carry-on.http://www.trackspoles.com/travel.asp?A ... ravelStaff
As it turns out, I use it with a Nikon DSLR and the 70-300 lens.
Even if you choose another monopod, you may like the Tracks extension.
Addendum: I use the Slik SBH-120 Ball Head on top of this monopod. That works well.