Demand response (DR) is a critical and effective measure to stimulate demand side flexibility to interact with power grids. However, the conventional scope of DR with only electricity carrier cannot fully explore the interaction capability due to users' must-run loads. By integrating various forms of energy, smart energy hubs (SEHs) make it possible for more users to flexibly participate in DR programs. In this paper, we explore the flexibility of this novel vision, termed as integrated demand response (IDR). An SEH model is formulated comprised of various kinds of distributed energy resources (DERs) including plug-in electric vehicles (PEVs), photovoltaic systems and gas-fired micro-turbines. With the help of the internet of things technology, an SEH can manage these DERs to bid in electricity markets without violating electric load. In the SEH, a number of vehicle-to-grid (V2G)enabled PEVs are aggregated to act as a controllable battery storage, thereby further improving the responsive capability of IDR. A two-stage stochastic market bidding model is developed to schedule the operation of the SEH against the uncertainties in PEVs, solar power and market prices. Case studies based on real-world datasets illustrate the effectiveness and efficiency of the proposed market bidding framework.