Do you have a fixed front sight base? If so that will limit your options a bit since most single piece freefloat aluminum handguards won't fit. Daniel Defense makes a version of their RIS II handguard with a cut-out for the front sight base but it's pricey.
I'm a huge fan of Midwest Industries rails. You can get 10% off if you order via the mothership site with the code 'BETHESWITCH'. You can also find vendors that have discounts on gun.deals (that's the actual web address). I think BCM also makes a really nice rails, especially if you're looking for FDE rails, but you really have to look for them.