You want to buy a your first synthesizer, so you can use it in your composition.
I would have liked more information on how you'd be using the synth in your composition.
I'm gonna assume that you are a newbie. Read on.
I'd recommend Roland GAIA SH-01. http://www.roland.com/products/en/SH-01/
Reasons:
1) Subtractive Synth
2) Easy control layout.
3) Software Editor. (Sold Separately $100)
40 Hardware Synth. (this is personal)
Runners-Up; Novation UltraNova, M-Audio Venom. Main reason I don't recommend this is because it's more advanced with some deep editing & layout issues. Plus, not as intuative. If you are experienced then buy an UltraNova.
If you are not hell-bent on hardware synth then you can try/buy a soft synth at fraction of the price.
If you are interested in recording then read below. If not, no biggie.
DAW = Virtual Studio
You will need a sequencer and/or a DAW (Digital Audio Workstation) for your composition. There are two popular ways of doing this from home. Expaination of DAW; Back in the days (not really that long ago) if you wanted to record anything with a decent audio quality you'd have to go to a professional studio which IS and WAS very expensive for most ppl.
First, a harddisk recorder. Advantages of hardware is you have physical access to the recorder. Disadvantage is you have something physical. Making it harder to lug around, and harder to update. It's good to have one of these, but it's not REQUIRED. I use one when I don't want to start my computer. Mostly for scratch tracks. I'd recommend ZOOM R8 ($299), ZOOM R16 ($399), or ZOOM R24 ($499). I recommended these items because it will connect to your computer over the USB; and it works as an audio interface, and control surface! They work the same way, except more you spend more options you get. This way you have the option of spending your budget.
Second, program (DAW) you can use on your computer. Advantage is it lives inside your computer. Disadvantage is it lives inside your computer. I just want to say I'm a PC windows user. I don't own an Apple PC. So you understand that I'm geared towards PC, not Apple. I personally decided to go with PC because of lower cost, and easier accessibility to software and hardware. I would recommend Cakewalk's SONAR X1 (Producer) ($399) or Cakewalk SONAR X1 (Production Suite) ($499), Presonus Studio One 2 Professional ($399), Sony ACID Pro 7 ($299), Ableton Live 8.2 ($499) or Ableton Live 8.2 Suite ($799).
FL Studio ($299 for FL Studio Signature Bundle), Orion v8.5 ($249), Mackie Tracktion 3 Ultimate Bundle (no longer available but you can get the Tracktion 2 for $30 by registering at my.mackie.com/ or try http://my.mackie.com/products/tracktion/demov2.asp), MU.LAB (http://www.mutools.com/, free version is good way to try out a DAW), Zynewave Podium ($50), Cockos REAPER ($225 for Commercial Use).
I'd recommend you try the Tracktion 2, because it's cheap and easy to use! Sonar if you have the money to spend (buy the Suite, it's better). Podium is awesome, too.
I did not mention Avid Pro Tools 10 (it requires a dongle taking up USB space permanently, and it's overtly proprietary, $699), Propellerhead Reason 6 (requires a dongle), Steinberg Cubase (requires a dongle), Steinberg Nuendo 5 ($1800), MAGIX Samplitude, MAGIX Sequoia, MOTU Digital Performer 7 (MAC only, $495), Apple's Logic Pro 9 (MAC only), and etc. The reasons are cost, proprietary, MAC only, and etc.
GarageBand comes bundled with Apple PC if you want to use that if you have a MAC.
(take a breath)
SYNTHESIZERS
Subtractive Synth is dominant type of synth on the market.
Learn about different synths. Additive, FM, Modular, and etc.
SUMMARY
Now I'm gonna tie in the DAW and Synths.
With Soft Synths you can compose/program your music all inside your PC using DAW. Making your life that much eazier.
If want to learn how let me know.
Wish you luck!!!