Good Day! I've been using a jailbroken iphone for 2 years now, (Currently on 3GS), and I know what I use to get my tasks done, but I don't know anyone else who's modded their phone, so my experience is very limited.
Here are some of the things I like to do with my phone, and how. If you know a better way, or have something YOU like to do, please add it to this thread.
I keep track of upcoming appointments by using my work's exchange calendar, and LockInfo.
I take and share videos directly to email/ facebook with Qik Video Pro.
I take fun filtered pictures with Hipstamatic and Camera+.
I do Wifi network scanning with iNet Pro.
I use my device like a portable hard drive with Mobile Disc.
I use Logmein to remote control my home/client PCs.
Stanza ebook reader.
Pandora, because I can't be bothered to take the time to put music on my phone.
I play lots of games.
I use iBodger to manage my Warmachine army lists.
I use the RSA app so I don't need a hard token security key for work (any way to get THAT into the Lockinfo screen?)
I use MXTube to download songs/ video from youtube.
This is probably the area where I could get the greatest improvement. Aside from iTunes, is there a way that I can download music directly to my phone, and have it sync into my library, either via iTunes or CopyTrans?