After jailbreaking using evasi0n 6.1 untethered your iPhone, iPad or iPod you must be looking for some new things which you can do other than the normal things which you were doing before jailbreak. Why not add some new repos/sources?
When you open Cydia you can see option of Manage and there you can find the Sources that are installed by default like BigBoss and ModMyi.com etc. These repos or sources provide further tweaks and apps which you can download if you want. Once you add one source the tweaks related to that repo are available to install on Cydia. So we can say these repositories are actually small outlets/stores inside the main Cydia store.
Below I have given top 5 repos which you should install in order to gain access to many powerful apps, tweaks and themes for your jailbroken device. Against each sources I have also briefly mentioned which tweaks it provides and the URL you will need to add in Cydia. Adding a source is not difficult only go to Cydia =>Manage =>Sources =>Edit =>Add, give the url address of repo and tap Add Source.
If you are unable to add repos or sources in Cydia, you can check this post on How To Add Sources To Cydia.
List of Top 5 Sources You Must Install
1. iForce: Provides some some very useful apps that can be used for different sharing options between devices like AirBlue GPS, AirBlue Sharing, BTServiceManager, iBluever, iTether and Siri0us. Add this URL in Sources: http://apt.if0rce.com
2. BiteYourApple: This source provides some good tweaks like iFile, IAP Cracker, Springtomize 2, Infinidock, Celeste etc. Add this URL in sources: http://repo.biteyourapple.net
3. iCauseFX: Provides themes, apps and tweaks like Barrel 2, BBSettings, 3G Unrestrictor, UISettings, AdBlock, Insomnia Pro, Lockdown Proand LockInfo etc. Add this URL: http://repo.icausefx.com
4. P0dulo: Provides excellent collection of useful Cydia tweaks like Auto3G, Barrel, Graviboard, Gridlock, Infinidock, Infinifolders, Move LockScreen to Unlock, RetinaPad and Multifl0w etc. Add this URL in the Sources: http://p0dulo.com
5. PwnCenter: Provides many good themes, ringtones and wallpapers. Add URL in Sources: http://apt.pwncenter.com