Math apps

Note that free apps often have ads or might be limited in some way. Where I know of the ads or limitations, I have commented on them. Ads are usually clickable and will take you to a website. There is no guarantee that the site will be appropriate for students.

Addimals (Free) - a simple game that aims to have kids memorize their addition facts for single-digit addition.
Addition Coach (Free) - Helps students learn the relationship between objects and numbers by adding blocks to reach a specified total. See here for a review by math professor Tim Pelton of the University of Victoria, Canada. 
Grow Your Garden (Free) and Grow your Garden HD ($0.99, iPad only) - Add water to your plants (and subtract water from your watering cans) to solve puzzles and make your flowers grow. 
MathTappers: Find Sums (Free) - designed to help learners to make sense of addition (and subtraction as a related operation), and then to support them in developing accuracy and improving their speed. See here for my post about MathTappers.
Numbl ($0.99) - Addition game, adding single digits to make totals up to the mid 20's.  See my post about it here.
Sumbo 1.2 (Free, ads run across the top of the screen when you're connected to the internet) -  a challenging addition game. Slide your finger horizontally, vertically, or diagonally along the board of numbers to choose numbers that add up to the target sum.
Sums Stacker ($0.99) - a "mathematical puzzle [that] allows users to play with different representations of numbers, while developing their number sense to create strategies to help them solve problems."  See here for a review. From the same developer as Symmetry Shuffle.
 Zen of Ten ($0.99) -  Similar to Numbl, but you have to choose pairs of numbers that always add up to 10.


MathTappers: Multiples (Free) - designed first to help learners to make sense of multiplication and division with whole numbers, and then to support them in developing fluency while maintaining accuracy.  See here for my post about MathTappers.
Monty's Quest ($0.99) - multiplication facts. Three levels of difficulty. Answer correctly to move the mouse up the hill to the cheese. 

+, -, X, / 
Rocket Math HD ($0.99, iPad only) - Choose any combination of addition, subtraction, multiplication or division to work on, at one of three different skill levels. Built-in 'scratch pad' for those who need it to work out answers. 

Crazy Coins (Free)
Sticker Shop (Free)
Coins Genius ($0.99)
Coin Math  ($1.99)
Jungle Coins (iPad only, $2.99) (See here for more details about these 5 apps.)

MathTappers: Estimate Fractions (Free) - designed to help learners to build their intuitive understanding of fractions by helping them to relate fractions (both symbols and pictures) to the nearest half (e.g., 0, ½ 1, 1½, 2, etc.) and then to extend their understanding by challenging them to use fraction estimates in addition and subtraction problems. 
Oh no! Fractions (Free, iPad only) Compare and visualize two fractions and guess which one is greater.  

Telling Time
Jungle Time ($2.99) - A talking clock reads the questions aloud and confirms the time when you set the clock. Settings allow you to control the level of difficulty. The hands on the clock move like a real clock - to get from 1:00 to 4:00 you have to move the minute hand around and around, not just move the hour hand.
MathTappers: ClockMaster (Free) - A variety of options available for helping kids learn to tell the time using both analog and digital clocks.  See here for my post about MathTappers.

Pearl Diver (Free) - number lines (Lobster Diver seems to be the same game) *HD version available for iPad. Work on number lines from 1-10, then negative versus positive numbers, followed by fractions. 
Splash Math - five different levels: first, second, third, fourth and fifth grade (ages 6-11) The iPod versions are cheaper ($4.99) than the iPad ones ($9.99). Although they are expensive, each app is also available as a free, limited, version, giving you a chance to try before you buy. They cover all the skills typically covered in a US elementary school at those five grade levels and are aligned to the Common Core standards.  They are intended as review apps rather than teaching apps - the app description refers to them as 'worksheets'. Each app will track the progress of up to six students and send email regular progress reports.
Symmetry Shuffle 1.0.1 ($1.99) - Slide, flip, and turn shapes. Work on spatial reasoning and geometry. From the same developer as Sums Stacker.

I've started a spreadsheet to keep more detailed track of math apps I've found that I think are worth using with students in grades K-5 (ages 5-11). There is a brief description of each app and I am slowly adding the Common Core standards that I think each one addresses. Bear in mind that I'm a language teacher, not a math teacher, so please let me know if you find any errors!