Satechi Smart Travel Router or even Apple's Airport Express router which are pretty nifty devices on their own.
But why carry an additional device that takes space if your notebook PC can do the same thing with help of the Connectify software. It essentially will create a virtual copy of your Laptop's wifi card to act as a virtual wifi hotspot which can use any of your PC's network interface that has internet access, to share the internet with other wireless devices. You can name the SSID as you wish and add a password and monitor which devices are connected. It currently costs $24 instead of the usual $40. A try-out version with limited functionality is also available to download at their website.