Tethering with PDANet
I tether in moderation to avoid killing the 3G network bandwidth. I'm paying $30 monthly for 3G bandwidth unlimited at a 5Gig volume alottment. I feel that this tethering is my right within this bandwidth and I reserve this right. I use PDANet, which I paid $30 (one time) for and have had a great experience with. (Some hit or miss connectivity at times, but mostly reliable.)
Sync with gCal using NemusSync
This app will sync all of your online google calendars with your iphone's calendar. This is all too convenient.
Stream your Video with Qik
Qik.com accepts your streams from their iPhone app Qik. The quality isn't as high as Cycorder but the video will be available LIVE on qik.com and that's awesome for all kinds of fun. Qik has an official version in the app store now that the 3GS will shoot video but I think if you have a 3G you'll need the version that you can install from Cydia. (Cydia is the installer for the apps of the jailbroken world. It's installed by default when you jailbreak your phone.)
Shoot Video with Cycorder
Great quality for a pocket recorder the cycorder video lacks options but records video like a champ. Just remember, for important moments of video, switch to airplane mode because a call will corrupt your currently recording video. Nothing like feeling hate when a great friend just calls to say, "hi".
Upload Video or Photos with PixelPipe and PPVideoEnabler
PixelPipe lets you route your media that you upload from your phone. Pictures are available in the media list by default but PPVideoEnabler makes your cycorder videos show up in that list too.
Put Apps in the Background with Backgrounder
Backgrounder allows you to drop an app to the background to let it continue to run its process. If you don't mind the additional consumed resources this app can come in really handy. One app at a time makes it hard to multitask. Fix that with Backgrounder.
Browse your iPhone like a Disk when on the same WiFi Network
This is a beautiful thing for me. I can hit any directory to store or grab any file on the iPhone by browsing the phone like a connected drive any time my phone and my computer are on the same open WiFi network. This is handy for the quick grab of media files or storing any file in any open or encrypted state on my phone for safe keeping and portability.
Extra Dock Icon with FiveIconDock
Because who has time to push the Home key to get back to the Home screen all the time.
SSH from your iPhone
If you are a tech savvy user and don't fear the terminal, SSH via the iphone in the jailbroken iPhone's terminal app, can really be a powerful way to access servers in an emergency. Imagine shelling into your server from 27E for a quick apache restart just before your flight takes off.
Really? Jailbreaking is Scary.
Yea, I know I could live without any of these features. But why? I bought the hardware, and I'm inclined to set it free! It helps to have a little experience with technology if you are going to undertake this. But the guys over at iphone-dev.org have made this so extremely easy. Download the app, run it, do what it says, tada... jailbroken! I can still use the app store and I'm really missing no functionality that the official service or hardware offers while adding a ton of flexibility, which I enjoy. The drawback to jailbreaking is that I have to go through this process anytime I want to do an official Apple iPhone OS Update. I just skip them most of the time. This can cause security vulnerability or missing out on official upgraded features. But, until the iPhone is everything I think it should be out-of-the-box, I'll feel ripped off knowing it has the potential to do more than it's being allowed to do.