Depending on the vendor, hygiene like for example HTC has a nice dialrer and a really nice keyboard so some of the suggestions here could be redundent depending on your phone manufacturer:

1) Dialer One – www.appbrain.com/app/kz.mek.DialerOne –  A dialer replacement.  Makes it really easy to dial bases on names.

2) SwiftKey – www.appbrain.com/app/com.touchtype.swiftkey.trial -A keyboard replacement.  Very good auto correct and prediction.

3) Handcent – www.appbrain.com/app/com.handcent.nextsms – An SMS app replacement. Extreamly useful.

4) FlightView-  www.appbrain.com/app/com.flightview.flightview_free –  If you’re a frequent flyer or know people who fly, website this is a great tool to track flights !

5) Google Voice – www.appbrain.com/app/com.google.android.apps.googlevoice – Why use the stock voicemail the carrier gives you when you can have all the google voice  benefits  ?!

I’ll keep this post updated.

Want to suggest an app ? use the comment section.  Thanks.