Spectrasonics Atmosphere
I discovered this synth several years ago and it has become a staple in all my tracks since. It has the most lush pads, goregous strings, and bizarre (but very useful) soundscapes. I love it. I highly recommend this package. It's sound library is HUGE -- gigs upon gigs of samples. It's amazing.

Cakewalk Dimension
This is a part of Project 5 and is basically a very versatile and easy-to-use sampler. It has a wide array of programming capabilities and filters. I am using this more and more instead of VSampler 3, and I have completely eliminated the need for an outboard sampler (I used to own an E-Mu E6400, but it had many many problems and bugs, so I'm glad to move to software based sampling). Cakewalk offers "Dimension Pro" which has a very large sample library. I may upgrade to it someday. Not yet, though. My wallet is getting too thin...

Cakewalk Rapture
I haven't used this yet as I just ordered it. I will post a review after I've had a chance to play with it for a while. The online examples sounded excellent, so I'm expecting a lot!

Pentagon I
In my opinion, this is the fattest and most versatile virtual synth I have ever seen. The range of sounds possible with this instrument is absolutely mind boggling. I haven't used it a whole lot yet just because it has taken me some time to learn how to get the sound I envision out of it. This is not a criticism! I love a challenge and the end result is well worth it. This is a great buy.

ReFX Juno X2
This synth apparently started out simply as a Roland Alpha Juno emulator, but grew to be much more. Before Roland sued ReFX and forced them to stop selling it, it was turning into its own very versatile synth. The sound is not as warm as a real Alpha Juno (of which I am quite familiar), but it makes up from the lack of analoginess with a load of extra filters and a thick thick thick chorus. This is a great treasure that I'm sad to see not for sale anymore. As if Roland is doing anything with the Alpha Junos anymore... Couldn't they have reached a licensing agreement for the name?

VSampler
This plug-in is a software sampler (obviously). It acts more like a hardware sampler than Dimension, which has advantages and disadvantages. I use it mainly to open sample libraries made for hardware samplers or competing software samplers (like Halion), since it can import practically anything. It is very powerful, but Dimension's elegant interface, gorgeous sound, and lack of bugs makes me want to use it more than VSampler.

There are more synths, of course, included with Cakewalk and Project 5, and I will post more about them in the future. I also use a wide array of freeware synths I have picked up over the years, each bringing something very unique to the table, and I will also post about them in the future.