[kennywinker]

Arturia microbrute is a great first analog monosynth.

The Arturia microfreak is an interesting new digital synth in a similar form factor.

The Yamaha Reface CS is an 8-voice virtual analog synth with a very understandable layout. Basically a juno 106 in an apartment-sized form factor.

As someone else mentioned, the volcas are a great starting point, and the korg monologue has an oscilloscope built in that makes learning sound design surprisingly understandable.

Just my opinion, but I think you should stay away from the Roland Boutique synths. I found them very unpleasant to use and not inspiring at all. I have not used the 808/909 drum machine boutiques - they may be better.

You can always go vintage. E.g. Some of the 2000s grooveboxes (electribes, various roland mc-xxx things) can be had for $100-200 on craigslist, and will be a ton of fun.