As Android allows you to get Apps from different sources, there are also some alternative Market applications. AppBrain even analyzes your installed apps and recommends other apps which might fit your user profile.
The internal keyboard of Android 2.1 is great already. It does its job and supports the voice recognition. AnySoftKeyboard looks promising but in real world use, I found it a bit awkward - esp. switching to numeric keyboard and back. Also it occupies more screen space. My favorite for now is the HTC_IME, a copy of the HTC Sense keyboard. It has various settings, supports all features of the internal keyboard (and lots more!!) and the compact mode is good for people with manly fingers.
I had K9 in use for a while until I realized I don't need to move mails around to other folders on-the-go and don't use the few special features of K9. I like the combined Inbox feature of the stock E-Mail app more and also the fact that it shows mails from my company's Exchange server. The Google Mail app makes nice use of GMail's special features and complements the stock E-Mail app.
As I have my own OpenFire Server at home which provides Jabber-Transports to all my networks (e.g. AIM, MSN, ICQ, Facebook), I needed a sleek Jabber/XMPP client for Android. Jabbroid seems to fit. It hangs sometimes a few seconds, but in overall, it looks good.
MyPod also seemed to be fine, but the interface was a mess with all those colorful buttons. dPod seems fine for Video podcasts. Google Listen is nice for Audio podcasts.