Depending on your ios there are plenty of safe and trusted sources. Honestly most of the stuff you find on here will be safe. It's all just regular people who love their device. If it's a new one and your 4.2.1 then redsnow will be your choice. I think the current version is 0.9.6rc8, I use it for tethered JB and it works just fine. here are a few links
That's all you need for current version, if earlier version search the developer forums, you can trust everything on here, people will tell you if something is malicious, also if you do a google search for this stuff, you will see the links are right up at the top of the search result....Hope that helps