I am new and unsure what the safest source of the various JB downloads.

What sites do you all trust?

Thanks.

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

Redsnow Download/Homepage

Dev-Team Blog

scroll 3/4 way down and look for:

• PLEASE UPGRADE TO iTunes 10.1 FOR BEST RESULTS
• WINDOWS 7 USERS SHOULD RUN redsn0w IN “XP COMPATIBILITY” MODE
• Make sure you’re using a USB 2.0 port

• OS X
• Windows
  

Click on windows and download the product. You will then need the correct ipsw, again if ios is 4.2.1 then go to the link below to download that file:

iOS 4.2.1 IPSW Download | iPad, iPhone 4/3GS/3G, iPod Touch 4G/3G/2G

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