About half the weight of the faster 300mm f/2.8L Canon lens, and a lot less costly. You still get the long focal length and dual-mode image stabilization.
Standout Spec: Maximum magnification 1:4.3, pretty good for a long tele.
Pentax-DA 55–300mm f/4–5.8 ED
Pentax 300mm f/4 DA* SDM
Sigma 70–300mm f/4–5.6 DG OS
Sigma 300mm f/2.8 EX APO DG HSM
Tamron 70-300mm f/4-5.6 LD Macro