Choosing The Best FE Exam Calculator: 2017 Update
The top calculators for the FE Exam are:
These are the three models that are still readily available (if you happen to have one of the older models then I suspect you're fully versed in the model and I would stick with it). If you want to know more, and better yet HOW TO USE THAT CALCULATOR TO PASS THE FE EXAM ... then read on.
If you're in preparation mode, see the growing collection FE Exam Prep Free Courses and the collection FE Sample Questions.
 FX115 ES Plus
 TI36X Pro
 HP 35S
These are the three models that are still readily available (if you happen to have one of the older models then I suspect you're fully versed in the model and I would stick with it). If you want to know more, and better yet HOW TO USE THAT CALCULATOR TO PASS THE FE EXAM ... then read on.
If you're in preparation mode, see the growing collection FE Exam Prep Free Courses and the collection FE Sample Questions.
There are countless ways to prepare for the FE exam, but we are going to focus on just one: your calculator strategy. Calculators are obviously an important part of the FE exam and make a big difference in the time spent per question. You still need to use your head if you are going to get the most out of them so here are the ways to make sure your calculator becomes your best friend.
NCEES Approved Calculators
NCEES publishes a list of acceptable calculators on their website, and for 2017 it looks like this:
Casio
 FX115 models, that means any FX115 including the MS, MS Plus, MS SR, ES and the ES Plus.
There are a number of models but you'll have trouble finding a model other than the ES Plus. So it's really not worth discussing the other models as the ES Plus has a far better screen than the older MS models.
Texas Instruments
 TI30X and TI36X, that includes many versions like the a, aSE IIB, IIS Pro etc.
Both of the TI's are still on the market and readily available. The 36X is a little more money because it has a far superior display screen.
Hewlett Packard
 HP 33S and the HP 35S
The 35S has replaced the 33S with a far better model so again it's not really worth the discussion of past models. You'll have a tough time even finding a 33S. They've upgraded it for a reason ... it's just better than the older 33S launched in 2003.
Note, both of these calculators are defaulted to the RPN system (Reverse Polar Notation ... 5 enter, 5 +, equals 10). and it takes a bit to get used to. I like it better but it has a learning curve so if you're short of time, do not go this route.
UPDATE: I've been informed you can change both of these calculators to the standard Algebraic Notation like a standard calculator.
UPDATE: I've been made aware there are HP calculators available on the internet that have useful formulas preloaded for the FE exam and PE exam. I haven't heard any feedback on them yet and they seem expensive.
Know Your Calculator
You're not going to get a clear winner because all these options are great, they.all handle:
So the real power is knowing how to do this with you're choice of calculator. And we'll get more into this as we develop this article further in the next coming weeks .... but here's a start .....
 matrix operations
 linear systems of equations
 interpolation
 numerically solve definite derivatives and integrals
So the real power is knowing how to do this with you're choice of calculator. And we'll get more into this as we develop this article further in the next coming weeks .... but here's a start .....
FX115 ES Plus Calculator Tutorials
Logarithmic EquationsA useful calculator tutorial outlining how to solve logarithmic equations for unknown variables. This is done quickly using the solve function for the Casio calculator.

Solving PermutationsIn the word "Calculator", how many ten letter arrangements are possible, with no repetition, if the first letter is a vowel. Be careful as there are two vowels.

Solving MatricesThis is a longer 10 minute video that solves addition, subtraction, multiplication and division operations with matrices. Once you store a matrix, it's critical to be able to recall it and perform another operation. A great video.

Complex NumbersHow to simply complex number expressions and perform basic functions with complex numbers using the fx115. Be sure your calculator is in complex mode.

Definite Integrals 
Definite Derivatives 
This video is another long one that we split into two parts. This part involves solving definite integrals. This material will be on your exam and it's good to know how to use the calculator to do the work for you.

This is the second part of the video that works with solving definite integrals. Definite, meaning we are solving the equation for a certain numbers, rather than solving generally. Don't wait until during the exam to become familiar with this great feature of the calculator.

Video sources include EquaterTV YouTube Channel, and Joel Erway's YouTube Channel.
HP35S Calculator Tutorials
This is a nice simulator we found deep in the depths of the inter webs and walks you through:
 solving vector equations and the corresponding geometry
 solving matrix determinants and basic operations with matrices
 the time value of money and interest calculations
 beam stresses
 solving a system of linear equations
 a series of electricity examples