Here are a list of sources for Cydia (some are by default):
- BigBoss & Planet-iPhone: http://apt.bigboss.us.com/repofiles/cydia/
- ModMyiFone: http://modmyifone.com/repo/
- Ste Packaging: http://repo.smxy.org/cydia/apt/
- iSpazio: http://ispaziorepo.com/cydia/apt
- Telesphoreo Tangelo: http://apt.saurik.com/
- ZodTTD: http://www.zodttd.com/repo/cydia/

Other notables:
- intelliborn: http://intelliborn.com/cydia
- FreeCoder: http://iphone.freecoder.org/apt/
- Hack&Dev.org: http://iphone.hackndev.org/apt/
- SaladSoft: http://nickplee.com/cydiasource/
- Urbanfanatics.com: http://urbanfanatics.com/cydia/
- iPhoneCake: http://cake.mapleidea.com/cydia/
- WeiPhone: http://app.weiphone.com/cydia/
- iFoneTec: http://app.ifonetec.com/cydia/
- iSpazio: http://ispaziorepo.com/cydia/apt
- Andy Dam: http://repo.gafoogle.com/
- Steffwiz: http://steffwiz.webs.com/iPhone/Repo

To add sources: Launch Cydia—>Manage—>Sources—>Edit—>Add—>enter the URL—>click Add Source

Here are the sources for Installer 4 so far:
- RiP Dev - http://i.ripdev.com/
- BigBoss’s Apps and Things. - http://apptapp.thebigboss.org/repofiles/installer4/
- iSpazio Official - http://repo.neolinus.org/ispazio/
- Ste Packaging - http://repo.smxy.org/installer4/
- ClubiFone - http://www.clubifone.com/repo/
- iPhone-notes.de - http://sendowski.de/iphone/
- a27 Dev Team: http://a27dev.com/installer/repo/
- Hackmyiphone: http://hackmyiphone.net/installer/
- Wildcat: http://iphone.handheld.com.vn/installer
- iClarified: http://installer.iClarified.com
- Modmyifone: http://i.modmyifone.com/

To add sources: Launch Installer 4—>Sources—>Edit—>click the “+”—>type in source URL—>click Done