Here is a quick listing on some of the useful Rails gems and plugin that I use in our projects everyday.
1 ) live_validation
2 ) open_flash_chart
Charts and graphs are always a headache to generate, but there is an awesome plugin which will make our job very easy. Generating a flash chart on ROR is pretty easy now.
3 ) will_paginate
This plugin or gem is very famous and one of the best ways to handle pagination in the web page
you can find more information on how to use this gem or plugin in Ryan Bates railcasts episode.
4 ) prawn_to
This plugin can be used to generate pdf documents without any sweat, I recommend this one over pdf-writer since this has better performance than pdf-writer.
5 ) auth_logic
This is a plugin to handle authentication, this plugin gives more freedom to customize your login system than the restul_authentication which I found very hard to understand and customize.
6 ) calender_date_select
Provides a calender popup for selecting a date. Supports internationalization and many other options to customize the display and format for our requirement.
7 ) faker and populator
Some times you might want to generate some fake data in your database with fake names, email or phone numbers with some sensible data instead of some random data which is not readable. Faker gem helps you to produce proper names, email address, phone number and so on. You can write a rake file to do the populate tasks and simply run the rake command to populate the data.
8 ) paperclip
Paperclip is an awesome rails gem. It is one of many gems(available as plugin too but gem is preferable to use) currently available that cater for file uploading and thumb nailing.
9 ) Autocomplete
Autocomplete is the most common feature we see now-a-days in some famous sites like Google,Youtube and so on. It is very easy to implement that feature with this plugin, I am also planning to release a blog on how to customize this plugin for some specific requirements. (Since the documentation on how to use this plugin is not sufficient)
There are many other useful plugins and gems are available as well. I listed only a few and I request readers to post the plugins that they found useful. This way, this blog post can act as rails plugin directory and helps developers to easily pick based on their needs.