Extended Logging Report

The built in logging reports are designed to find out about individual transactions and don't cope with Batch or long running transactions. The extended logging report allows you to view all email address changes made this month (for example) or to see the changes made by an import job

CiviCRM Error Handler

Sometimes CiviCRM can be real tough to debug. Especially when you are getting fatal errors, but only by some users, and you can't recreate the problems. This utility will send you a detailed email when a CiviCRM fatal error occurs.

Mandrill Email

This extension provides email delivery for CiviMail and/or other email from CiviCRM via the Mandrill service. Mandrill is an email service that runs on the email infrastructure that powers MailChimp. It is a high quality, low cost option for email delivery, with no loss of delivery functionality, quality or performance in comparison with alternatives. 

Stripe Payment Processor

Stripe Payment Processor for CiviCRM.
Stripe is a wonderful payment processor that eliminates much of the headache for PCI compliance.  Stripe.js securely transmits card details from browsers to Stripe.
Stripe is free to try, requiring only an email address and password to get started.
Stripe is also has no monthly fees, your costs are a small per-transaction fee + 2.9%.
It handles regular contributions as well as recurring through Stripe's subscription/plan feature.