Hey, I just recently (in the past few months) got a Yamaha TX7 off ebay. The TX7 is the module (I think that's what they call it) version of the DX7. It's basically the DX7 without a keyboard. I highly recommend it. Look up the DX7/TX7 online, it gets rave reviews everywhere and is/was the best-selling synth of all time. You might find a DX7 on ebay, but I would suggest looking for the TX7 first. Not as many people look for the TX7, because it doesn't come with a keyboard, but that just means they sell for less. I think the DX7 was selling for ~$200+ on ebay, while I got the TX7 for about $120. You can edit/create patches using JSynthLib, one of the only free (and by far the best) DX7/TX7 editor/librarians online. I've been using my sister's keyboard to control it and I'm currently looking for a midi controller to use with it. In the end, I'll probably end up spending about as much as a DX7, but from what I've noticed there seems to be a lot less competition for the TX7. Anyway, if you're still looking for a synth, I would highly recommend you look at this one.
As far as computer vs. stand-alone goes there are pros and cons to each (as usual

) With computer synths (or VSTs as I believe they are called) you can get classic synths for a fraction of the price and without any maintenance involved. However, there will be diehards who will tell you that there is a difference in sound between a vst and the "real thing", much like people who prefer tube amps to solid state amps. I would recommend trying both at your music store (if they have a decent selection of synths for you to play with.) Another thing I did when researching synths was to look up the synths on youtube and listen to people playing the synths I was interested in. Some synths may not look like they can do much, but listening to them may prove otherwise.
Hope this helps! Let me know how the search is going...