Ed already hit on some really good ones, and I agree with him that you won't find much of anything for under 500 new that would be of good quality.
Occasionally you will see a Korg X5D or a Yamaha S03 near that price ( look for something like Musician's Friends Blem or B stock ). Both of these are wav based romplers that seem to play fairly well ( you could check Harmony Central's synth database for opinions ). I doubt that either are going to be outstanding for synth leads and ambient sounds, but I'm sure either will give you basics to work with for both.
Like Ed, at 500 Usd, I might recommend software, because at that price, notwithstanding that you'll need a controller and a midi / audio inteface, I think you'll do a lot better soundwise by adding one quality commercial module and a bunch of freewares.
I like all of the commercial offerings Ed recommended, especially Absynth and Oddity and the Arturia synths. I also would add Imposocar to that list. I will add a few more ideas too.
Korg legacy collection package has everything you need soundwise at 499, and it includes a controller, but of course you still need the audio / midi interface, so it will go over your budget a bit. M Audio still makes the Audiophile 24 / 96, and even though it's a few years old now, it still is rated very highly for value vs dollar. It can be had for about 100 Usd.
Knowing what I do now, if I have to start from scratch with $500 as my absolute budget, and my main concern is good leads and ambient patches... here's what I would likely do:
Get the Audiophile: 100 Usd
Go to a pawn shop or some other discount place ( maybe even a yard sale if ya get real lucky ) and buy the cheapest midi kb ( that still works of course ) and use it a my controller until I can afford something better. If you're lucky enough... you might pay less than 50 bucks, but lets say you have to spend 75.
325 left.
The first thing I'm buying is RGC Audio's Pentagon 1. An absolute killer analog modeler that can be had for about 120 Usd or so and maybe less if you look hard enough. It's right at the top of the user ratings at KVR Audio for good reason. Value vs dollar, I haven't tried anything better ( I've tried most of 'em too ). If you don't need acoustic instrument sounds, you might want to bundle it with Z3ta ( also from RGC Audio ) which is a wavetable based synth. The bundle price is 240 usd or so. Talk about ambient sounds, Z3ta is a killer. You'd still have about 80 bucks or so left, and there are plenty of synths in the 50-75 Usd price range that would work too.
But.. let's say you do need some acoustic sounds.
Then I might go for Pentagon ( again 120 )
and add Luxonix Ravity S for about 130 or so. Ravity gives a good account of itself in most areas for a wide array of acoustic and synth sounds. With the 75 left over.. I might go for Superwave performer, which is like a junior Z3ta at about half the price ( approx 70 Usd ).
Then you can add freeware:
Green Oak Crystal- One of the best
Ichira Toda's Synth 1 - Outstanding analog modeler based somewhat on a Nord Lead. You'll need to d/l some of the external ( free ) add on patch banks for it, as the internal presets are of fair quality.
Superwave P8- baby brother of Performer.
Ugo texture- Very nice FM / analog modeled synth.
Any of the Killer series.. For when you want an analog modeler with attitude and are not feeling so "ambient"
Mik Sybrandt series of softsynths. Excellent for freeware. Even has a very decent drawbar organ emulation.
Add a couple of free software effects from Kjaerhaus ( the reverb and chorus emulations in particular are very good ), and a vst host and you're set. There are sveral freeware hosts that will work fine, but you could also add something like Xlutop Chainer ( 50 Usd or so ) and maybe use the freeware Supewave P8 insstead of the commercial Superwave Performer.
If you are interested in the soft route, I'd suggest a look at KVR-Audio's site.
http://www.kvraudio.com/ They have it all there and much more.
AJ
[This message has been edited by Bluezplayer (edited 11-08-2005).]