The Particle Zoo
This 5-pack contains a Higgs Boson, Z Boson, W Boson, Gluon, and Photon. The W Boson is double-sided (it's both W- and W+).
Approximately 3.5 lb (1.6 kg).
For ages 5 and up as it contains glued-on/small parts.
The Boson 5-pack is available in a lightweight shipping saver version which is especially nice if you live outside the U.S. All 5 plushes will be filled with lightweight stuffing. Of course you won't get the full effect of their varying weightiness, but they will be the same in every other way.