Just within Thinkfinity.org, there are thousands of resources to practice math and reading so I can give you some general ideas, but if you post what grade level or age your child/student is I can provide you more specific math and reading websites.
Two of my daughters' (ages 7 and 11) favorite math websites are Concentration from Illuminations where they can match numbers, shapes, fractions, or multiplication facts and AplusMath where they can practice math skills through games, flashcard and worksheets.
Then, both of my daughters' teachers (grades 1st and 5th) bring their students to Power Proofreading to help them with reading, writing, grammar, puctuation and spelling skills.
Let us know specifically what math and reading skills you are looking for or the age of your child/student and we can provide age appropriate suggestions.
First grade is a wonderful grade since it seems like this is where kids' really click with reading and math skills. I taught first grade and it was amazing to witness their growth from the begining of the year till the end. Many come in just learning their letters/sounds through alphabet books and by the end they are reading mini chapter books (Frog and Toad). I bet your first graders will really enjoy the Electric Company website.
As for first grade math resources, your kids would benefit from practicing addition/subtraction with the interactive called What's Under the Shell. A fun way to learn about shapes is to have the students make a quilt or just make a pattern using the Patch Tool.