Lost Platoon features vehicles, making it a great map for epic firefight sessions.
Last but certainly not least, the mother of all Halo achievements, Endure. To get this whopper, you need to survive four sets of firefight (meaning you must make it to set five) on Heroic difficulty. The best advice I can give you is to be patient, and practice a lot. This achievement will take hours and you will most likely fail multiple times. There are two popular maps for this achievement. The first is Lost Platoon. Vehicles are your friends in this map. Have two people take the warthog and keep the petal to the metal at all times. Keep driving around the building and focus on taking out larger threats first. Choppers are probably the highest on the list, followed by Grunts or Brutes wielding fuel rods. Go easy on the roadkills since hitting Brutes and Hunters will do damage to your vehicle. The other two should defend the top of the building and take out the wraiths with the laser. Reserve the laser for the wraiths only or you'll run into trouble. The warthog crew should try to free up choppers for the two on the building. A good tactic is to move the freed choppers to the bottom of the main staircase (where the warthog spawns) so they're out of the way and they're easy to get to when you respawn. Make sure you leave the laser on the building though, otherwise you may lose track of it and you won't be able to get to it when you need it. When you have multiple vehicles running, it is wise to coordinate which direction you circle the building. A head on collision between a chopper and warthog will often result in a death or two.
Use Alpha Site's two major choke points to your advantage.
The second map is Alpha Site. For this map, you'll pair up and each take a set of stairs. Stay in the main lobby and take out enemies as they funnel through the bottlenecks. At the beginning of each round, I like to pop as many Grunts in the head with the pistol as possible as they head down that first staircase from the platform they land on. That requires you to leave the lobby for a bit but you're not too far out that you should run into any big trouble. Speaking of popping Grunt heads, I recommend turning on the Grunt Birthday Party skull so Grunts explode when you get a headshot. Besides the wacky comic relief, they also give you a few free kills since their explosion is enough to take out other grunts close by and explode any grenades sitting on the ground. But back to Alpha Site. Communication is key in Alpha Site since the four of you will be fighting in pretty close quarters. If you start getting overrun, make sure everyone backs up so you're not catching each other's grenades. During bonus rounds, you can usually take out quite a few Grunts as they come out the windows above the elevators on either side. When they start piling up in the lobby, use pistols and carbines to rack up the headshots as those will give you a lot of points. Use all your grenades as well since there will be plenty laying around when the bonus round is over.
Again, this achievement takes a lot of work, and most people agree that this is the toughest achievement in any Halo game. Communicate well, know your role, and try your best to stay alive. Most of all, be patient. If you need professional help with this one, SIP has you covered with their Team Punishment (private forum, join SIP for access). We also have a thread in our forums for all Halo 3: ODST meetups.
I can haz the recons?
Once you've hammered down all these wonderful achievements, head to Bungie.net to unlock your shiny new recon armor. You'll need to create an account and link your gamertag if you haven't already. On your service record you should see a banner with all the Vidmaster Challenge emblems and a button to unlock your armor. Once that's done, jump back into Halo 3 and check out your new gear. I hope all that hard work was worth it!