in the cheesiest way possible it would probably need to be polyphonic. because otherwise i couldnt do chords and all that.... i want it to sound like IT IS a synth (so i guess the mini-moogs are some kind of suggestion)... i wandered around soho soundhouse yesterday and played with some. didnt really bond with anyone. the moog was quite fun, but looked a bit fiddly....
Well, the moog you played with was monophonic, like the majority of analog synths. It's very difficult to build a synth with a useful amount of polyphony using analog electronics, because each note of polyphony needs to have it's own synth architecture - so a 10-note polyphonic synth is really 10 seperate synths with a common control system. A few were built at the end of the 70s, and are now regarded as classics - the Prophet 5, the Jupiter 8, Memorymoog and the Oberheim OB series - but they are large, unwieldy and prone to breaking down a lot. They're also extremely expensive. Buying any of those synths 2nd hand now will cost you well over a grand.
Because polyphonic synths weren't really around in the 70s, most of the classic synth sounds and playing styles you associate with analog synths were developed through monophonic playing - in fact, a lot of purist synth players regarded the arrival of polyphony as the start of some kind of decline. Before that, synths were exotic hybrid instruments - using the front panel controls, players could shape the pitch and timbre of the tone after a note was played, or even treat pitch, timbre and amplitude as completely separate characteristics. This approach produced sounds that were more akin to a lead guitar or a saxophone than to any kind of keyboard instrument, but with a much greater control over timbre. When polyphonic synths appeared (so the argument goes), players got sidetracked with chords and lost this experimental edge, and the possibilities of synth playing got gradually narrowed down until synths became, essentially, souped-up electric pianos.
So, yes, think about what kind of stuff you want to play, and how you want to use it. But you say you want a synth that sounds like a synth - which I guess means the classic subtractive architecture (modulators>>oscillator>>filter>>amplifier) that you associate with analog synthesis. In that case, you've really got 3 options:
Virtual Analog
Virtual analog synths are digital devices programmed to behave like classic analog synth circuits. They first appeared in the mid 90s and nowadays there are lots to choose from. Because these kinds of synths are essentially just DSP chips running code, Edward is quite right in saying that they are effectively purpose-built computers, and it's true that buying a software synth program to run on a normal PC will generally get you the same sounds for less money. But there's also the inspiration factor to consider - IMO, really good instruments should inspire you to play them and create new sounds, and a lot of people just don't find it inspiring to sit at a computer. I know several producers who don't use computers for music, because they associate computers with mundane, repetitive, non-creative tasks and an alienating work enviroment that they don't want in thier studio. There's obviously still a big market for hardware synths so maybe quite a lot of people feel this way.
In terms of sound quality, virtual analog synths have come a long way in the last 10 years as programmers have developed their skills, and some of the newer ones are really excellent. They also typically have features that are impractical to implement on real analog synths, such as patch memories, sequencing and onboard effects. Virtual analog synths can be monophonic or polyphonic at the flick of a switch, because it's really all just a case of reallocating DSP resources.
Monophonic Analog
As I said, most real anolog synths are monophonic, and it's perfectly possible to spend a huge wedge of money on a vintage analog monophonic synth - however, there are also lots of cheap-and-cheerful older synths around that won't cost a fortune. You can get synths like the EDP Wasp or the Roland SH-101 2nd hand for a few hundred quid - they're immediate, they sound great, they've been used on loads of classic records. Reliability isn't such an issue with these devices because the circuits are relatively simple, so they don't break down as often and when they do they're easier to fix.
There are also several really good monophonic analog synths currently in production. Because of dance culture's fondness for classic analog sounds, there has been a renaissance in analog design over the last 10 years - although most modern analogs come as rack modules, so you'd need an external MIDI keyboard. But MIDI keyboards are pretty cheap to buy, and you could use it for other things, like triggering samples on your computer as you suggested.
The analog vs. digital debate is never very far from the surface when people are comparing synths, and it's inevitable this thread will touch on it. Ultimately, you need to try out several synths of different designs and see which ones you prefer. For what it's worth though, here's my opinion. As I said, in terms of sound quality I don't think there's much to choose between a well-programmed digital model of an analog synth, and an actual analog circuit - and if you do the FFT tests, you can prove that objectively. But what makes analog synths so inspiring to use is the immediacy of thier user interface: like a guitar amp, all the controls are physically coupled to the sound itself, so you feel like you're controlling an instrument in real time. Once you start adding things like patch memories and multitimbrality, you begin to abstract that process, until what you end up with is more of a production tool than an instrument. If you want something that makes you want to sit down and play, and that's fun, you may end up going with a real analog synth.
Polyphonic Analog
As I said already, this is the most impractical route to go down. For a start, there are no polyphonic analogs currently being made, so you'd need to get a vintage model from the late 70s/early 80s. You can get some Japanese synths from that era without spending too much money (such as the Roland Junos or the JX8P) - but anything American that's worth having will cost you a fortune.
One final tip - if you decide to get something 2nd hand, go on the American Ebay site and find someone prepared to ship to the UK. The exchange rate is ridiculous at the moment, about 2 dollars to the pound, so even once you've factored in shipping costs and a voltage convertor you'll still save a lot of money.
Hope that helps.