The best advice I've heard is SCHEDULE IT. Date night. Even if it's not a date night out, with a sitter and nice dinner...sometimes DH and I just get a library movie or NetFlix rental and cuddle up on the couch.
For us, doing THE DEED has been scarce since we have a 6, 5 and infant. I think sometimes you just are in "survival mode" and relish sleep or family time more than the S.E.X. It's not that we don't miss it, but like you, it just doesn't happen.
I do think a date night with a sitter once a month is important tho. Whether it's a paid sitter, overnighter with Grandma and Grandpa, etc. If you don't have one, find a good sitter in a neighbor, church friend or local community college. I find "adults" better than high schoolers who can be immature, inexperienced and not available.
Try not to be so focused on the S.E.X. Focus on cuddling, spending quality time together and having conversations that don't involve the kids or work.