Below is a list of the types of search engines by topic. Within each category there are several engines to choose from.
Some indexes are more extensive than others.
You'll just have to try them to see what works best for you. If there is a search engines that is not here let us know. Contact Oscar Nierstrasz for more information. The popular Yahoo features a hierarchically organised subject tree. The UK Index is a manually maintained index of resources in the UK Alta Vista has access to 8 billion words in 16 million web pages.