Pretty much every good electrical store has 110v transformers. First, check the wattage of the appliances you plan connecting to ensure you get a powerful but not too large/bulky one.

To give an idea of a few transformers typically available at least here in Ireland:

• 40 watt - about the size of a power adapter for a PC desktop speaker system or scanner. This will suit most set-top boxes, assuming you just plug in one at a time. Just make sure the wattage does not exceed 40 watts.
• 100 watt - around the size of a 6-volt lantern battery. This will handle a couple of set-top boxes, so long as the sum of their wattages do not exceed 100 watts.
• 800+ watt inverter - around the size of a 6-volt lantern battery. These will typically handle appliances with heating elements, such as coffee percolators, irons, toasters and so on. However, as most of these inverters do not have good voltage regulation, these may not be suitable for any electronic items, so make sure you read the item's description closely before you pick-up a high wattage convertor.

For those appliances compatible with 220-240 volts, just get a few travel adapters. These are available at pretty much any airport and many electrical stores also. Shaver adapters will generally cater for the 2-pin appliances.

Finally, if you bring any surge protection leads over, do not use these without a transformer, even if the appliances you plug in are 220v-240v compatible, as the high voltage will burn out the surge protection circuitry that is designed for 110v. However, there should be no issue using a surge protection lead plugged into a tranformer such as for hooking up a handful of 110v appliances to a transformer.