Depends on what kind of music you want to make
Pop - Logic does good on it's own
House - again Logic does pretty darn good on its own, sylenth1
Dubstep - NI Massive, sylenth1
Trance - Zeta+, Sylenth1, FXspanion Synth Squad, Omnisphere
Country/rock - audio interface with real instruments
Best reverbs - ValhallaRoom, ArtsAcousticReverb
Best compressor - Waves SSL stuff
Other - Sausage Fattener is a great limiter/distortion plugin
Best mastering - Waves, Izotope Ozone
I have quite a collection and these are what I end up with.
You can make the exact same sounds and apply the exact same effects with the DAW of your choice, these tools just make it faster to get the sound you want, and may improve performance before bouncing.
Depending on what you want to do depends on what you end up getting, also ensure that if you are using Logic Pro you will need plug-ins that use AU, if you use Ableton then you can use AU and VST, ProTools uses a proprietary RTAS plug-in format.