top 5 operas?

Tough to come up with a ranking because people's tastes are different.

To begin with start with Mozart's Don Giovanni, Magic Flute, and La Nozze di Figaro....

Eventually you should tackle Wagner's Ring and Tristan und Isolde, those are the top 5 for me, although tastes vary and you shouldn't quite start opera listening from Tristan, because most likely you won't enjoy it.

I can't make a decision on 5 operas, so I have picked my 4 favorite composers of operas and their works that I enjoy most:
1. Puccini: Tosca; La Boheme
2. Verdi: La Traviata; Rigoletto; Aida
3. Mozart: Don Giovanni; The Marriage of Figaro
4. Wagner: Gotterdammerung (or the entire Ring Cycle if you consider it as a single work); Tristan und Isolde

I'll gear mine for the novice. You'll enjoy these more:
1) Orff - Carmina Burina - untouchable
2) Carmen - Puccini - many selections you know
3) Gianni Schacchi - Puccini - hard to find, but worth it
4) & 5) Sdcampbell's Wagner and Verdi selections

Magic Flute
Marriage of Figaro
Porgy & Bess
Aida
La Boheme

Got to agree with a lot of the selections above. You did ask specifically about DVDs, opera being an audio/visual medium after all. So ...

1. Wagner's Gotterdammerung as part of the Pierre Boulez's full Ring Cycle on Phillips (Deutshe Grammophon also has a full Ring Cycle by James Levine and the Metroplitan Opera that they released on Laser Disk that is even better but only Die Walkure seems to have been released on DVD for some reason).

2. Mozart's Die Zauberflote (the Magic Flute) on Deutshe Grammophon by James Levine and the Metroplitan Opera

3. Puccini's Madam Butterfly by Martin Scorsese on Sony (this one isn't just a simple presentation of the opera but is more broad in its presentation)

4. Verdi's La Traviata by France Zeffirelli on Universal. Again this is not simply a stage performance.

5. An off the wall choice (to make 5 selections) - The Who's Tommy by Ken Russel on Columbia. It's wild

Well, the Levine Ring Cycle is released on DVD this month. Change my fav from the Boulez to the Levine cycle please (although the Boulez cycle is interesting because it is presented at Bayreuth, the home of the Ring, and has some interesting, sometimes wierd, interpretations).

After reviewing the Levine and Boulez cycles on DVD I see that both of them have their strengths and weaknesses. One should start with Levine's but Boulez is better on the acting side I believe. It is just the sound and video quality that really kill Boulez edition.