1. Use Rightscale. You can get away with the free edition, but for $500/month the basic paid edition will allow you access to arrays and all the excellent scripts available on the marketplace.
2. The front end. I would strongly suggest moving away from ELB. We are using it and are about to get rid of it. The main problem is what exactly happened last night. If a whole AZ goes down, the ELB for that zone can get screwed and the DNS was not updating the CNAME to remove the bad zone. Instead of ELB, we have our own LB solution we are going to roll out that will use Rightscale server arrays and will handle the updating of the DNS names itself. We also aren't going to use Route53, because we learned last night that the API for that can go down and you can get stuck with bad DNS records.
3. Application servers. Use at least 3 AZ and have them evenly spaced. This is easy to do in Rightscale with sever arrays. Make sure your voting ration for scaling isn't 50% because you might not scale correctly if you loose 2 AZ. Keep the vote to 30% and you will be happy (if one zone votes to grow, let it grow).
4. Database. This is the fun one. We have been using MongoDB with pretty good success. Our multi-shard DB has 3 servers per replica set and has them distributed equally between AZs. We use 4 EBS drive RAID-0 drives for storage which have had problems in the past due to the outages that EBS sometimes has. Our best bet has been a watcher process that will kill the mongod process if there's any problems writing to the drive array. By doing this, the replica set will automatically failover to the next server and we won't get stuck with a primary node that can't write back to disk. For backups, we just freeze the writes on the secondaries and do EBS snapshots even 15 minutes. Rightscale has some great EBS tools for managing this for you. If you loose a server, we can deploy a new server in a matter of minutes and it will rebuild the RAID array from the last backup so we have a warm spare.
5. Monitor, monitor, monitor. Rightscale has some great tools for monitoring everything. Use them, and use more monitoring on other infrastructure (ie Pingdom)
Doing something like this will cost a lot more that just sticking to a single AZ, but you should be able to survive one, if not two complete datacenter outages.