Unique 30th Bday location LA
The Roof Bar at the Standard downtown is a pretty dramatic/Bladerunner-ish/top-of-a-skyscraper location for drinks and appetizer-ish kind of food. To be honest, don't really remember the food but certainly eatable and location is amazing.
Benihana -- never been but really curious to go -- "an experience at every table"
Medieval Times -- again, never been and but ever since renting Cable-Guy am dying to try.
Since Korean BBQ was mentioned why not go to Manna, you really cant beat the price at $15.00/person. If you can splurge a little more then I think the 3 course tasting menu at Opus for $30.00/person might be a great way to celebrate a 30th bday. I dont know, I really <3 that place!
In the south bay, how about Belacan for some awesome Malaysian food? Big room reminiscent of a dim sum place in SGV, and has a "safe side" to its menu so that you can order your basic fried rice and curries, but has a host of Malaysian specialties like Belacan Crab (!!) that will wow the whole table. Servings are huge so it's easy to walk out of there for less if you order family style.
You could do Dar Maghreb for a unique eat-with-your-hands, belly-dancing dinner.
Also, Ethiopian restaurants on Fairfax.
Palms Thai for the Elvis.
Do dim sum or Chinese banquet for cheap.
Could also do Korean BBQ for fun.
Don't know if they can easily accommodate groups of 20, but you might look into a few of the Sawtelle restaurants as well.
There is a great restaurant in Silverlake called Malo that has a menu of things that are mostly under 10 bucks. You can reserve a large table on the patio in advance. Then, if you are so inclined, there is a cool bar call Akbar half a block to the west on the same side of the street that has great music and no cover before 10 most nights. Good luck!