Google. Google just completely revamped and improved their patent capabilities.

I would also suggest Google Patents

The site is easy to use, the cross references, in terms of other patents that cite that patent are good and they provide both a text version and a PDF version that is downloadable, of the original patent with all tables and a link to any drawings filed with the patents.

Some sites don’t go back all that far and I don’t know how far Google goes back. Sometimes, hen I miss my dad, I do a Google patent search on him, it’s kind nerdy I guess, but they have all of his, back to 1963. And, I just popped in 1833 into the search and got one hit, at least. So Google’s database goes back at least that far, but I don’t know how complete their database is, in terms of the much older patents.

Your local Patent and Trademark Resource Center should be able to help. You can also search for European patents online.