CoolMath's website uses the unit circle to teach about radians and degrees of a circle. Colorful tutorials also teach about sines and cosines, and practice problems with solutions are provided as well. CoolMath also has a tutorial page with practice problems for the trigonometry of circles which includes the formula for the arc length of a circle in radians and degrees, and the sector areas of circles in radians and degrees.
A virtual unit circle allows students to measure angles of a circle visually, in radians or degrees, at MathLearning's website. This site also has a quiz about radians and degrees. OnlineMathLearning has several videos on the topic of converting between radians and degrees, and radian measurement. This website also has a page with information about radians and degrees that includes common angles in both degree and radian measurements.
Quizlet has over 60 flashcard sets for the topic of radians and degrees. Each flashcard set includes virtual flashcards with audio, as well as printable flashcards for use offline. There are also printable worksheets and quizzes with answers, in addition to virtual quizzes and worksheets with audio, which can be helpful for pronunciation purposes. The quizzes on this site are customizable. Educators and students can also make their own radian and degree flashcards, worksheets and quiz sets on this site.
SoftSchools has a trigonometry calculator that allows students to enter the radian or degrees of an angle, while the sines, cosines, tangents, cotangents, secants and cosecants are also displayed. Quia's website has several radian and degree games available. Radian and degree versions of Concentration, matching games and word search puzzles are all available at the Quia site, in addition to flashcards in Javascript and HTML.