Cooky, it would be helpful if you could give us more information such as what type of music you do and what plugins and sounds you use as there's many different kinds of equipment that are more suitable for some jobs than other stuff.
However, there's three basic ways I can think of doing things the way you want...
1) Use audio backing tracks along with live keyboards... That's easy but not ideal.
2) Sample the sound on your computer into a sampler or sampling keyboard... This is capable of good results but can be very time consuming.
3) (And this is the one I would choose.) Forget the sounds on your computer and either find similar patches or recreate them on hardware synths.
As for what kind of synths you need, that depends very much on what kind of music you do and what kind of sounds you use. A good 'all-rounder' option would be one of the workstation type synths from the likes of Korg (the M3 or M50), Roland (the Fantom, Juno-G or Juno Stage) and Yamaha (Motif or MM). There are also a large variety of very capable second hand workstations available such as the Alesis Fusion. Workstations are usually sample based synths (though the Alesis Fusion has several kinds of synthesis in addition to sample based) so they can be good if you need sounds that are based on real instruments though they can do electronic style sounds too (but as they're sample based, they're not quite as versatile as VA or analogue synths for that stuff)... If you don't need full workstation features (sequencer and maybe audio recording) there are synths available which don't have those features though they sometimes lack other features that you may find useful.
If your music is more electronic in style then analogue and vitual analogue synths may be well worth a look. There are lots of these about... Available from the likes of Access (Virus), Alesis (Micron), Clavia (the Nord range) Korg (Radias and Microkorg) and loads more, it would be impossible to list them all! For real analogue theres Dave Smith instruments (Mopho, Tetra and Prophet) as well as many others including loads available second hand.
If your music is more beat based then the Akai MPC series will be worth looking into.
Have a look at the Keyboard
And Keyboard workstation
reviews on this very site to see what's about.