I would highly recommend 'Nicholas & Alexandra' & 'The Millionairess', these are two of his finest earlier roles together with 'Sinbad'. After that perhaps 'The Vault Of Horror', 'Randall & Hopkirk Deceased', 'Life and Loves of a She Devil', 'Monarch Of The Glen' and the episode of 'Black Adder II' he was in called 'Potato'. The 'Silver Chair' is quite fun too. As far as I'm aware these are all available on DVD.
His appearance in films such as 'Curse of King Tuts Tomb' and 'Curse of Frankenstein' are fairly brief and can be seen on YouTube, which incidently is a great place to find some of Toms other roles.
In short, If you haven't seen it, Nicholas and Alexandra is a great place to start.
I hope this has helped.