I was a huge fan of Titanium Backup back in the day! When I first started with Android I was probably in the Android Market downloading apps as often as anything else on my phone. I eventually ended up with a pretty impressive arsenal of over 200 apps, over 3/4s of which I never used more than once. After the first several Rom installs on my DroidX I eventually discovered Titanium Backup. I tried out the free version going and backing up each individual file then meticulously restoring each one after the Rom install. Each time I managed to slim down my app stockpile of apps letting go of the ones I knew I didn't need with cries of pain and agony like a true horder. Eventually I sprung for the paid version which made things a heck of alot easier but remained time consuming as it would still take 10 minutes or more to backup, and then another 10 minutes or more to restore the apps, making a Rom install last for nearly 30 minutes. This became such a headache that I finally reconciled to maintain only enough apps that I could quickly grab from the Android market directly after each Rom install. To this day I use only about 15 apps total, but not anymore!
With the latest update Titanium has made the task of backing up and restoring apps and app data easier and more timely than ever! The new update includes the ability to backup apps + data in the form of a flashable.zip that can be flashed along with the Rom. Both user and system apps are supported, and there are options to backup apps+data, apps only, or data only. I can finally return to my days of app browsing!
Free: Titanium Backup
Pro: Titanium Backup Pro