I have spent alot of time recently playing Persona 3 and watching the Persona 4 endurance run and I was wondering what other Shin Megami Tensei games are worth playing.  I have heard alot about Digital Devil Saga and Nocturne, but I want hear what you all have to say before I invest since they are still full price on amazon.

SMT: Nocturne is probably my favorite. DDS, well, it's quite short and the ending is a cliffhanger so you do kinda need to buy them both. Get nocturne though, it's so amazing.

That one where it's pokemon is pretty fun... Devil Summoner I think it is. 
 
Devil Survivor is also pretty good if you have a DS.

" That one where it's pokemon is pretty fun... Devil Summoner I think it is.  Devil Survivor is also pretty good if you have a DS. "

I enjoyed Devil Summoner 2.  It doesn't have the great cast of characters like the Persona games but the action rpg style battles are fun, and the story is interesting.

" @Akrid said:

" That one where it's pokemon is pretty fun... Devil Summoner I think it is.  Devil Survivor is also pretty good if you have a DS. "

all of them are pokemon with the exception of digital devil saga  the original SMT, back in the SNES area, was pokemon as well ;) "

It depends. There's a bunch of games under the SMT wing but they all vary in style.  
 
While I would suggest Nocturne and Digital Devil Saga 1 and 2, they're both unforgivingly hard. Devil Summoner 1 and 2 play pretty differently than other games in the SMT franchise but are also terrific games, so I'd heartily recommend those-- especially the second one. 
 
Devil Survivor is a pretty good tactics game and Strange Journey is probably my favorite RPG on the DS, so you'd also be well-off with either of those. 
 
Honestly, though, if your only experience with SMT is the Persona series, then play Devil Summoner 1 and 2. You'll get the oh-so-terrific style that the rest of the SMT franchise has and you'll get to get the grips on the actual roster of demons and fusion. Once you've gotten through that and think you're ready for a greater challenge, then I definitely recommend Nocturne. It's brutally hard but it's the best one in the franchise, IMO.

If you're interested in more Persona games, Persona 1 is on PSP and Persona 2 is being ported to the PSP as well. They differ quite a bit from Persona 3 and 4, but they are still good. A lot of people like Nocturne. Personally, I think it's one of the weaker SMT games. Even saying that, I still think it's very good. Plus, you can use Dante from Devil May Cry as one of your demons.
 
The two most recent Devil Summoner games are great. They have real-time combat though, so if you are looking for more turned based games you may not want to try them. I also really like the two Digital Devil Saga games. You really need to play both in order to get the full story, which is unfortunate, but if you have both they are great games.

I have DDS and DDS2. Can't say DDS have lived up to my expectations so far, but I've heard DDS2 is much better. Not played any other SMT except for the MMO (which is fine if you like asian F2P MMO's, it's got some of the SMT stuff in it like Jack Frost for example) and the PSP remake of Persona 1 (which is nowhere as good as Persona 3 and 4, but not bad).

Yo, I hear Persona 4 is cool... 
 
I've only played P3/P4, but from what I hear they're all good, depending on how tolerant you are of old-ass games. P1 for PS1 and/or for PSP might be difficult to get into due to its old school feel.

Im going to assume that Devil Summoner is a difficult game to find since it's 140 dollars new on amazon right now and devil summoner 2 is 80...

Play both Digital Devil Saga games. While hard, they are probably the less frustrating SMT games around. The gameplay and story are awesome. They are among my favorite games of all time. Be sure to check them out!

If you think you have the patience for it then you should try Strange Journey.