Multimedia
From Google
Goggles : Use pictures to search web, just amazing. A visual search application, instead of using words, take a picture and search. Works very well with logo’s. one of my top favorites. More info
Google Goggles
Ringtone
Ringdroid : Easy way to make ring tones from songs we have. More info ringdroid
Picture editor
Picsay : Quick and effective way to add effects to pictures from mobile. More info Picsay
Radio
A Online Radio : Excellent way to listen online radio stations aor
Communication
SMS
Handcent SMS : found it better than the native message application. More info handcent
SMS Backup : useful to backup sms messages to gmail with a separate label android-sms
Voice
Sipdroid : SIP/VOIP client, very useful application especially to connect and make calls with your sip provider like action voip. : More info : sipdroid.org
Networking and System tools
SSH
Connectbot An easy way to establish ssh connection, support ssh key generation and public key authentication.connect bot
Monitoring
NagMonDroid Nice application to connect to your nagios instance and display short summary. I found it very useful to get my server status while i am on road :) More info :nagios page
CIDR
CIDR calculator Very useful IP subnet calculator. More info : CIDR Androidlib