There are a lot of themes on Cydia, so many, you'd probably be there for days trying them all. The problem with most of them is that they're so damn ugly. Jaku is one of those gems hidden away in Cydia. It is by far my most favourite theme for the iPhone and probably the best theme for the iPhone. The icons have been meticulously handcrafted for every default iOS app by William Szilveszter.
William doesn't just stop there however. He has also handcrafted new icons for over 100 3rd party applications from the Appstore. The theme he states nearly took him a year to make, now that's dedication for you. It's been exclusively made for the retina display so the only devices supported are the iPhone 4/4S and the iPod Touch 4G.
You can find it in Cydia for $2.99 which is a small price to pay for such a fantastic theme. Recommended for anyone with a jailbroken device.
Below [click on the image to enlarge] are just some of the icons made for the theme.