There have been some other good answers here, but there are some other measures that can be useful too. In fact, not all of these are particularly technical.
As others have pointed out, adding a passcode to your iPad will allow for full system encryption, which prevents anyone from stealing data from the device. Combining this with auto-lock and auto-wipe provides a decent level of security against a thief. For the most part, your average thief is more interested in selling the iPad on for some cash, so they're likely to just do a factory reset and wipe it.
If your device has a SIM card, it works on the same principle as a mobile phone (cellphone), which means that a thief may be able to use the device on the network and charge payments to your billing account. The absolute best defence against this is to call your provider and have the SIM blocked.
They may also be able to register the IMEI number of the device on a blacklist, which works across all networks. This causes the device to display "IMEI Locked" and halt whenever it tries to join a network, regardless of which SIM card is used. Furthermore, most police forces will check IMEI numbers of any devices found during raids of criminals' houses against the database, in order to further indict the criminal for theft and recover property. In most countries it is an offence to change the IMEI number of the device in order to evade a block, and in the UK it carries a prison sentence. Whilst this won't get you your iPad back, it'll make it very difficult for the thief to sell it on.
The iCloud and "Find My iPad" apps are useful for simple location identification, but these are unlikely to be trusted by police as they can be inaccurate. For example, there was a case in 2011 where UK police kicked down someone's door in a search for a stolen iPhone, and it turned out that the location information was wrong - the phone was actually two houses down the road. This ended up with the home owner suing the police force for damages. It's just not safe for police to rely on that kind of data. However, it can be useful in contributing to the body of evidence, which is a technical term for an array of evidence that all points to a particular address or culprit.
On the flipside, remote wipe is an excellent feature. If the thief is sloppy when going about their work, they may end up powering the device on whilst it has an available internet connection (e.g. via WiFi or 3G) and the remote wipe will automatically kick in once the device phones home. This also provides evidence for police, because cell tower geolocation and traffic timestamps are cached.
Finally, there's insurance. If you purchased the iPad on contract, often your provider will have an insurance option that covers against theft. This will cost you a monthly fee (how much depends on your contract) but will usually result in a brand new iPad being sent to you if yours is stolen. Usually they ask for a police incident number as proof of theft, but other than that there's very little hassle involved. You can also use a 3rd party insurance company (Protect Your Bubble specialises in personal devices, but there are many other companies out there) to insure against theft. Typically these offer better cover, including accidental damage, water damage, etc.
But, of course, the best option is not to have it stolen in the first place! There are iPad lock cables available that allow you to physically tether your device to an object to make it difficult to steal, much like a Kensington lock that you'd use on a laptop. These only take a few seconds to set up and are ideal for situations like leaving your iPad in a hotel room. Combined with a passcode and auto-lock, this should be a reasonable deterrent to most thieves.