Vibratechnics make some of the worthwhile ones and they cost shed loads...
Vibratechnics Mk2/Mk3 Gearbox Mount £65.00
Vibratechnics Mk2/Mk3 Gearbox Mount Competition £70.00
Vibratechnics Mk3 16v Front Engine Mount £120.00
Vibratechnics Mk3 Front Engine Mount Competition £130.00
Vibratechnics Mk3 R/H Engine Mount £60.00
Vibratechnics Mk3 R/H Engine Mount Competition £75.00
Vibratechnics Mk3 VR6 Mount £120.00
you can but cheaper (and nastier) poly ones but i personally wouldn't bother as they make the engine too rigid, creating loads of unwanted vibration and noise.