So many to pick from:

Brivity

Contactually

eEdge

Kunversion

Seize The Market

Vulcan 7

Top Producer

Team Leads

Wise Agent

Market Leader

The best one is the one you will use every day.

Outlook would probably be the answer to your criteria.

    Outlook is the least expensive CRM "software" that is out there.

Anna,

We devised our own.

Be careful out there.  Most agents invest in CRM's that are far more than what is needed. I have used Outlook, excel and other systems I create to work with Outlook and it works fine for me and my business - 15 years and counting.

The most efficient, simple and inexpensive CRM app may be sitting on your computer already. Which email client are you using?

What do you want to do with a CRM?

Use an Excel Spreadsheet and manually maintain it. That is about as cheap as it gets.

Gmail, MSN, Yahoo, even Outlook already installed on your puter are available to you. Some find Excel to be all that they need to manage their database and execute CRM type functions.

There a a couple DOZEN vendors of CRM that have FREE versions such as BellaRuby.com, SugarCRM.com and Hubspot.com

The question that must be asked is what do you need your CRM to do for your business? What will your business need your CRM to do in five years?

Be aware, the greatest cost of ANY CRM, free or otherwise, is the setup, validation, training and implementationj. Most agents, after making this HUGE investment stop looking and conform their business to the ability of the CRM. Not good.

List the essential features you will need in five years and then meaningful recommendations can be made.

You have many answers here.

Well, simple and inexpensive may not be the most efficient.  Finding the system that works for you and that you will actually use on a consistent basis is the best.   I keep things simple and try to be as consistent as possible with that message. 

I never used CRM software.... didn't need to...

Then you need Buffini & Company's  

Referral Maker CRM

I use Wise Agent and like it! Have heard good things about Realty Juggler. No one CRM is the best IMO as it depends on what you want and what you do with it

I love Brivity and would caution you that the change is costly (timewise) down the road. The system has everything you could need and is very user-friendly!

I used a few and just wasted money and time. Now i'm tasting Lion Desk. It is affordable but quite mighty. 

Most efficient

Inexpensive

CRM

Those three do not go together. 

Realty Juggler - $99 per yr

Annette Lawrence has it summed up very well!

Love the points Annette Lawrence , Palm Harbor, FL 727-420-4041 made, especially this part:
Be aware, the greatest cost of ANY CRM, free or otherwise, is the setup, validation, training and implementationj. Most agents, after making this HUGE investment stop looking and conform their business to the ability of the CRM. Not good.

I hope your dreams come true.

I successfully used Top Producer for many years but it is not simple.

Even me, I found in answers so many new for me.

I have Outlook and Top Producer.

I would say look into outlook.

Anya Turchin - nothing to beat ReferralMaker CRM from Buffini & Company 

IMO get one built into a website and kill 2 birds with one stone!

Problem solved!

Good luck.

I've tried Realty Juggler. It seemed to have the features I was looking for but I didn't have the time to set it up and implement. I'll consider going back when I find the time.

There are many choices.  Though, typically you get what you pay for and what you are willing to spend the time on to learn and setup.

Richard Weeks nailed this one!

What is most efficient, simple and cost-effective depends on what you want to accomplish with your CRM.

Mine is reasonable and part of my Market Leader package.

Liondesk has worked well for me. 

iPhone-notes

Excel

sticky notes on the wall

on a paper note pad

Unless your office mandated you to have Agent achieve I will be hesitant to recommend you anything.

Following...

I made my own simple one

Excel.

Realty Juggler at $99 a year. Wonderful tutorials and links to Mail Chimp among other things.