Some great repos for iphone/ipod touch are.
HTTP://cydia.xsellize.com
HTTP://cydia.hackulo.us
HTTP://sinfuliphonerepo.com
These repos will allow you to have cydia store apps for free. App store apps for free. And the best themes and mods for free.
Make sure your iPod is jailbroken to do this.
Then goto cydia->manage->sources->Add
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Recent jailbreaks are
Greenpois0n
This will allow you to jailbreak 4.2,4.2.1 firmware. And it is untethered.

Mods
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Some good mods are
Sbsettings
Five column springboard
Cydelete
File
Myos
Winterboard
Infinifolders
Android lock
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Themes.
Some good themes are
Mp2
Iflat
Illume
Glasklart