Two things that are always impressive for a chemistry lab are color change and bubbling. So two reaction rate labs that I can suggest are the reaction of bleach with solutions of food coloring and also the reaction of acetic acid with sodium bicarbonate.
First, a little general information on reaction rates. The rate of reaction is defined as the change in concentration of one of the chemicals over time. Since measuring concentration directly "on the fly" as a reaction is occurring is difficult, it is usually easier to measure the amount of time it takes for a reaction to go to completion. Since we are dealing with very visible chemical reactions, it will be easy to time them with a stopwatch and determine when they are complete. Second, as you mentioned above, two factors relating to rate that are easy to alter are concentration and temperature. Those should be the variables you deal with here.
The first suggestion is the reaction of bleach with food coloring solutions. Food coloring is basically dye in water. Chemical dyes are organic molecules that have very strong light absorbing/reflecting properties. This is mostly due to the presence of networks of carbon-carbon and carbon-heteroatom (oxygen, nitrogen, etc.) double bonds. The sodium hypochlorite in bleach will oxidize and remove these double bonds, thus removing the color from the dye. Put a solution of food coloring in water in a glass beaker and use a stir plate with a magnetic stir bar to continuously stir the solution. Add a measured amount of a commercial bleach solution from a buret suspended above the beaker. The bleach will remove the color from the solution, leaving it colorless when the reaction is complete. Measure the time it takes for the solution to go colorless for the rate. You can run the reaction twice using pure bleach in one run and bleach diluted with water to see the effect of bleach concentration on the rate. You can also run the reaction twice using a hot food coloring solution versus a cold food coloring solution to see the effect of temperature on the rate. Make sure you add the same volume of bleach each time so that only one variable is changed with each run.
The second possibility is acetic acid and sodium bicarbonate. Again, put an aqueous solution of sodium bicarbonate stirring in the beaker and put the acetic acid in the buret. Mixing the two will produce carbon dioxide gas which will very visibly bubble from the solution. Again, altering the concentration of either chemical or the temperature of the solution on the beaker will show the effect on the reaction rate. Measure the time it takes for the reaction to go to completion by judging when the bubbling is complete.