I'm looking for something particularly like this
http://www.critterandguitari.com/products/pocket-piano-gr
with just some key basic modes and essential parameters (osc., tone filter).
Right now my favorite synth plugin is YMCK's magical8bitplug; I'd really like it if someone could recommend something with just a little more modes and features than that, but not so many that it becomes intimidating (I'm kinda new to synths and get scared easily).

 

There's no output on your Pocket Piano ???

And the price is very expensive... You can have a second hand Korg MicroKorg (Or maybe the XL one) for that price ! They are easy and some awesome sounds + VOCODEEEER (I love vocoders lol)

I had a MicroKorg I really miss it... It was very fun !

But regarding plugins I don't know... Most of them are complicated... The Arturia Oberheim is relatively easy to use.

Some friends will probably come and suggest you a few other things

Or :

FabFilter One

U-He TyrellN6

Maybe Native Instruments Massive

 

Not that basic , but not complex at all, very good soft synth.

http://www.lennardigital.com/modules/sylenth1/