I use a lot of manipulatives in my math stations. One is pattern blocks --in the beginning the students are just handling them and "playing" with them to get used to them. Then I add laminated picture cards where they have to match the blocks to the pattern. (I got those for free online). Another station is bears where they can count/sort/create patterns. I let them play with them for the first couple of weeks, then add laminated cards where they have to match the pattern or sort colors onto paper plates.
You can also use links--have them count, create patterns, and measure things around the room with them. A few students can be on the computer-math games, math on starfall. You can also have a math writing center where they write numbers, number words etc.
If you're working on addition/subtraction you can have another center where they can use counters/bears to complete math problems on a skillsheet.
I find groups of three or four work best--any more than that and they fight over the manipulatives. Mine are in no way cutesy or fancy--very simple and straightforward. And I explain the centers daily---tell them WHY they're working in that center. They should be able to answer the questions "What are you doing and why?" For example, "I'm using pattern blocks to create/copy a pattern". Admin in my school is really big on that: students knowing the focus/skill being taught.