I have been using an Android Dev Phone 1 for about a year now, and I should say I am very happy with it. Phones are not phones anymore, and the ability to run third party apps is quite crucial. Here in this post, I am going to list some apps that I have on my phone.
CallTrack. This app logs all the phone calls in a Google calendar of your choice. Why would I need my call log in a calendar? Well, I don't know yet; but I don't want to throw away my call log every time something happens to my phone (e.g. wipe user data, change the physical device, etc).
SMS Backup. This one copies to Gmail all the SMS messages you send and receive. It has proved quite useful to me. For example, you can do a Gmail search for a friend's name or email address and you will see the SMSes you sent to them or received from them, along with other emails and chats you had with them.
Notepad with Sync. I was using AK Notepad for quite some time. But I prefer Notepad with Sync for one reason: it syncs to the cloud. You need to sign up for a Helipad account. One more user name and password to remember, but at least my notes would be much safer on their servers than on my own SD card. Also, I can edit my notes on the phone as well from a computer, without having to copy files around.
Handcent SMS. Shows SMS messages in a popup and let me reply to or delete messages then and there, without having to switch to a different app. Quite useful to me, as I read and immediately delete about 80% of the SMSes I receive.
Twidroid. A full-featured Twitter client for Android. (Update: I am now using the Official Twitter app for Android.)
OI File Manager. Not something I use every day. But it's good to have a file browser installed, so you can, for example, install some app that you get from some source other than Android Market.