PAID:
Launcher Pro Plus (most features are free, but I had no trouble paying to support such a great launcher)
Root Explorer (useful, worth every penny, easy, and powerful)
Beautiful Widgets (didn't need it on the Droid X, but I HATE Weatherbug)
Pure Calendar Widget (absolute best calendar app/widget EVER, in my opinion)
FREE:
AutoKiller (makes other task killers looks absolutely silly - set to optimum)
Wireless Tether (awesome, but needs root)
Physx Live Wallpaper (a neat live wallpaper with very low system overhead)
Google Navigator (stock on other droids, but still a fave)
Tiny Flashlight + LED (I liked the motorola version better, but it didn't use the LED on this phone)
Barcode Scanner (by ZXing Team - this is very useful when you need it)
AutorunKiller (same dev as AutoKiller - I have this specifically kill one startup process on my phone: Verizon's 3G hotspot app)
Kindle (they have so many free and cheap books. Love this app)
Google Sky Map
Dolphin HD Browser
PDAnet (for the times when I can't do wifi and need to plug in)
Battery Status Widget (on desktop for exact percent amount)
Starfield 3D Live Wallpaper (total star trek, star wars, star anything geek)
Google Earth (how can you NOT love this with the GPU on this phone???)
Pandora Radio
Google Translate
Ringdroid
Red text = root required
Bold = Absolute must have, in my opinion
Some might disagree with some of my items, but it might be helpful.