I like ncaacasino.com. His nflcasino.com is awesome too. A cheap one I like is theeckelpool.com. It's only 5 bucks, but will have 1200+ people, so the payout is good, and there is second chance pools as well.
i will be finalizing one later this week with 20-50 entries probably if you're interested, I can send the info.
Enjoy March Madness.