CiviXero

This extension provides integration with Xero accounting package. It requires the supporting extension nz.co.fuzion.accountsync - more details are in the README file

General functionality

Email Address Corrector

Background
This extension was developed after an investigation of Future First's bounced email addresses. We found that many of our bounced emails contained the same handful of spelling errors (hotmai.com, hotmail.cpm, gmai.com etc). Although correcting them wasn't a time consuming process, there was concern about the opportunity cost, so we needed a system to prevent new errors being introduced.
 
What it does

Fancy Searches

Great custom search for searching and filtering on event participants in CiviCRM. Easily list just the participants who choose "session AAA"  from your priceset options and send them all an email or SMS/Text message.  Or get the total count of participants for priceset option "session BBB" so you know how many chairs and snacks you need to set up. 

Current Features: 

Show Contact Deceased

This extension has been incorporated into core as of CiviCRM 4.6, so the 4.5 version will not be updated.

This CiviCRM extension makes a single, simple change: it changes the name of a contact so that (deceased) appears in red after their name on the Contact Summary page. The intent is to enable CiviCRM users to avoid inappropriate communications where they inadvertently phone or email or write to a contact who is deceased.

Olark Chat

Olark is a chat service that enables web site visitors to chat with staff of an organization. It has a good set of features for services in this space (http://www.olark.com/features). This extension integrates the service with CiviCRM by posting chat transcripts as CiviCRM activities attached to the visitor's existing or newly created contact record and assigned to the relevant staff person's record.