Hi,
I buy lots of census, and the occasional microfiche. I would never buy from ebay as most of the genealogy stuff can be purchased cheaper from the original company at the same price.
If you want census stuff, I definitely recommend archivecdbooks, the quality is excellent. It all depends on how much you have to spend, and your involvement in this MAD hobby.
If you are that mad, then I would recommend a yearly subscription to Ancestry.com -it is really expensive, but pays dividends in your seaching.
BUT, first try all the free sites, eg BMD, family search (IGI) etc. etc.
I guess it depends on what you are looking for.
http://kevw.net/Essex-good-links.htm
I have a years subscription to Ancestry, and I will probably renew it, with maybe couple of months break.
Best
Kevan