How about some blue spot lights.
Check out the monster List- http://markbutler.8m.com/monsterlist.htm
There are plenty of links for haunt lighting.
One to look at would be the water proof black light, a good idea to highlight certain areas of your haunt.
I would suggest going with blue and green flood lights. The fixtures (the type that have a stake attached to drive into the ground) can be picked up at Home Depot for nearly nothing and you can daisy-chain several together. I wouldn't advise too many on one circuit though. Here is a link to a well respected prop builder's site: http://www.vilethings.com/id70.htm. Look at the pictures near the bottom of the page to see what effect both can have on a grave scene. Hope this helps.
...also, refer to this link to see what they look like.
Yeah, I bought a mini-strobe at Spirit Halloween the other day and intend to incorporate it's spooky effect in my yard haunt as well. I'm going to try to direct as much of the strobe away from the TOTs...I've heard it can affect some people differently i.e. siezures and what not.