I don't remember what my 5 were the first time I posted, but after having my Droid for almost 6 months, I'm sure they've changed.
1: Swype - Currently using the color-modded versions somebody posted .apk's for in another thread.
2: Handcent - I use this thing so much, the default messenger just doesn't seem right any more.
3: Seesmic - My Twitter app. I used to use Twidroid, but have found Seesmic to be far superior.
4: USA TV Guide - It allows you to see what's on tv up to 72 hours in advance. Program in the channels you want want to track and go. Find a show you want to watch, and it'll give you the standard TV Guide description, tell you when it originally aired (or if it's a new episode), and it gives you the option of setting a reminder.
5: Beautiful Widgets - The only app I've ever bought. It comes with a home (displays time, weather, date, and location), small home, and widgets for the quick activation / deactivation of bluetooth, gps, plane mode, silent, vibrate, wifi, and brightness controls.