Any processor ending with the letter "k," for example the i7-4770k. They are designed for overclocking, as they have an unlocked CPU multiplier. However, before you overclock you need to ensure your motherboard supports it. If your motherboard's chipset begins with the letter "z", for example the Z68, Z77, Z87, Z97 and etc. then you can overclock.
Also ensure compatibility between a processor and your motherboard; check your motherboard's manufacturer's CPU support list. Another example, the i7-4770k will only be compatible on chipsets where the first digit is a 8 or 9 (e.g. H87, B85, Z97 and etc.)
You could wait for Devil's Canyon (DC) if you desire, however personally I don't think they'll improve much over the current Haswell processors. The wait for DC shouldn't be long however, as it is stated to be released during mid-2014. Regardless I cannot guarantee compatibility with existing motherboards, unless you have a Z97 or H97, then you're safe.
All the best.