See:
http://www.hmrc.gov.uk/eis/
for general guidance. Take particular note of their comment that rules and tax treatment can change.
I have not used them, but have in the past used VCTs.
EIS schemes are generally thought to be higher-risk than generalist VCTs, but these days the VCT doesn't help you with IHT.
Consider also AIM shares (if you can get a list of John Lee's portfolio of AIM shares from his FT articles, you may find this a good start!) - not all AIM shares help with IHT.