Are we talking a list of series that a person should know about to have general knowledge of conversations/cosplay that might occur at a convention? If that is the case, the list would be changing every few years.
Currently (considering the above) I would say (in no order, also, no where near a list of favorites):
+The Melancholy of Haruhi Suzumiya
+Ouran High School Host Club
+Fruit's Basket
+Naruto
+Bleach
+One Piece
+Fullmetal Alchemist
+Death Note
+FLCL
+Neon Genesis Evangelion
While Ghibli works make up their fair share of the percentage portaying to "Anime you should know about," I wouldn't say the majority of con-goers have conversations or cosplay Ghibli characters. Haruhi Suzumiya and Ouran are two of the more popular modern series, naturally they will contribute to a fraction of the cosplay/discussions. Naruto and Bleach are still popular series, and they're released in English (no to mention the fact they appear on Cartoon Network). Ergo, they're more likely to be the subject of your everyday anime-fan attending a convention. One Piece and Fullmetal Alchemist also fall in with Naruto and Bleach (although, of the four, Fullmetal Alchemist and Naruto will recieve the most attention). Death Note is among the most popular manga (and now anime) with in the general scope of the anime fandom (new fans, old fans alike). FLCL is a cult classic, as well as Evangelion (however, these two will contribute less to cosplay and more to conversation, so they are simply necessary for conversation survivablity).
As a list for con newbies who want to focus more on the veteran conversations, I would suggest a few of the following:
+Royal Space Force - Wings of Honneamise (GAINAX, Sci-Fi)
+Legend of the Overfiend (Ero-anime)
+Akira
+Macross
+Gundam (Universal Century, I wouldn't worry with SEED or Alternate Century)
+Otaku no Video
+Bible Black (Ero-anime)
+Megazone 23 (Sci-Fi)
+Daicon IV Opening Animation (GAINAX, Japan Sci-Fi Convention)
+Outlaw Star
This is a list of series that are more "old school" and that you might here discussed by people who have more of an old-school interest or that are old school themselves.
I suggest both Bible Black and Legend of the Overfiend (Urotsukidouji) because they are two of the best know ero-anime (hentai) series. While Bible Black is the more recent of the two, it is popular among a few cosplayers (the school uniform). Urotsukidouji has been compared to Akira, in regards to the impact it had on anime fandom when it was released (in theaters).
Akira and Otaku no Video, IMO, are anime fan's "Must See" anime. Akira is a classic sci-fi movie that is responsible for a lot of anime's popularity among the older generations. Otaku no Video is one of GAINAX's finest works and gives a good view into the lives of Japanese Otaku (it is actually a parody of the starting of GAINAX). Megazone 23 can be thrown into this category, as it was one of the titles that raked in anime fans back in the day.
Macross and Gundam (UC) are two of the most well known (not to mention, Good) mecha franchises. If you can only catch a little of each, I suggest Mobile Suit Gundam (the original series, but if that is too long, watch the movies) and Macross: Do You Remember Love?.
Royal Space Force is the only anime movie I consider better than Grave of the Fireflies or Jin-Roh (in fact, watch Jin-Roh: The Wolf Brigade as well). Royal Space Force is a beautiful sci-fi movie, the first major anime title produced by GAINAX (if you can see the vein I'm running in, GAINAX has a lot of the classic titles).
Daicon IV Opening Animation. This animation, (
http://youtube.com/watch?v=rzy1RNJBUo4 ), was used for the opening of Daicon IV (the 1983 Japanese Sci-Fi con) and produced by what would become Studio GAINAX. It is the "sequel" to Daicon III's animation (
http://youtube.com/watch?v=6xLAVWf-N3c ).
Outlaw Star is a more modern "old school" anime, if you will. It is a gateway drug of sorts (got a lot of poeple I know into anime).
Outside of definitive anime series, a few video game series that might want to be addressed are:
+Guilty Gear
+Street Fighter
+Kingdom Hearts
+Metal Gear Solid
All for the reason of cosplay, mainly.
Edit//
I disagree with what TomtheFanboy has said about Gundam Wing being the best Gundam Choice. If you want to get a feel for what Gundam really is, I suggest the Universal Century hands down. While Gundam Wing is a very good AC series, it doesn't hold the same water as say Mobile Suit Gundam or Char's Counterattack does. Gundam Wing, however, is one of the better known Gundam series.
I do agree with your suggestions of Vampire Hunter D, Record of the Lodoss War and Sailor Moon. They're all classics in my book.
Edit #2//
A list of modern series that people having conversations about fansubbed anime are mostlikely to talk about:
+Lucky Star
+Tengen Toppa Gurren Lagann
+Code Geasse
+Seirei no Moribito
+Terra E (Terra E is also a sci-fi classic, as in, the original Terra E)
+Hayate no Gotoku!
+Sayonara Zetsubou Sensei
+Dennou Coil
+School Days
+Evangelion: Rebuild (Not out yet)
Lucky Star is the newest work by Kyoto Animation (Haruhi Suzumiya, AIR). Gurren-Lagann is Gainax's newest mecha series. Code Geasse is quite popular, but I don't follow it (check Wiki). Seirei no Moribito is based on the fantasy book of the same name and is absolutely beautiful (a new show, Shugurui is also beautiful but not as popular yet). Terra E is a remake of the classic manga of the same name (there is also a classic movie as well). Hayate no Gotoku! is about a combat bulter and is a comedy series (it is another series I am not following closely, so Wiki). Dennou Coil is a ghibli-esque cyperpunk series. School Days and Sayonara Zetsubou Sensei are both part of the Summer '07 season, the former is based on a dating sim and the latter is a completely random dystopian series.
Evangelion: Rebuild refers to the 4 new Evangelion movies that will be released between '07 and '08. They are not out yet, but the trailer can be easily found on youtube for the first movie. The first 3 movies of Rebuild will retell the Evangelion story and the last one will feature a new story. This will definitely be a hot topic until all 4 are finally released.
