It depends if you want to make use of over 1C charging or not. What those before me have suggested work fine for 1C charging.
However, if you wish to charge at 2C (1/2 hour charge times from flat), or more, you'll need to go 12V only, as chargers with built-in power supplies have low power capabilities. E.G. The UDC30 only has a 50W maximum power output and a 5A maximum charge rate.
Something like a
Hyperion 720i has a maximum power output of 250W, and a maximum charge rate of 20A. This means that you could charge one of those new Trakpower Dark series packs (say the 5000mAh 40C one) at 5C to fully charge it from flat in 12 minutes.
It also has in-built balancing, but is better than the Core-RC charger in that it can utilise different balance boards.
The Core-RC charger has a balance board suitable for JST-XH plugs, whilst the Trakpowers traditionally use TP plugs, though JST-XH leads are available.
The Hyperion charger isn't that expensive, considering its capabilities, though bear in mind, if you haven't already got a power supply, you will need one for 230V use.
An option that is more widely available in the UK, is the Fusion range, from
Logic RC. These chargers range from a £60 12V and 230V input, 40W charger, to a £125 12V only, 180W charger. I use two of the Paladins, and I have to say, they really are excellent, and very easy to use. You can also charge more than one pack at a time (as you can with any charger that can do 4S or more), but I needed it for 5S packs.