I use the Spotlight Search Engine built into Tiger (Mac OS X 10.4).

It has the advantage of being very quick. Like the old locate tool (somewhat obscure), it worked on a prebuilt index and therefore finds results very quickly. It sorts the results by type and relevance and is very easy to use. It pulls up web pages, email messages, files, entries in my outlining software, MP3s (by searching the ID3 tags) and so forth.

One downside so far is that it does not understand meta-data in image files. I have a large number of botanical sketches and I usually put species information and other things in the image comment fields. I would very much like a search for, for instance, "hederacea" to pull up images of Ivy-Leaved Morning Glory (Ipomoea hederacea) for instance, but it does not seem to be able to do that. It does seem to do this somewhat with photos stored in iPhoto, but not bare images. I get around this by putting the sketches in Notebook (Circus and Ponies) with the metadata in the Notebook fields. Spotlight pulls up the Notebook entry with a link to the sketches.

The Spotlight search returns results as you type the search text. Sometimes this is convenient, but other times it is distracting. I would like a preference to turn that feature off.

i selected other because ive used aol desktop search

I have google desktop and all i can say it's useless, what's the point in having a search engine when i've got probably about 80% of my files organized. In the rare occasion when i need to find a file i just use the windows search.
Google desktop opens 3 processes related to it and it uses about 10-15mb of memory overall.
The 'gadgets' are nice but there is no point, the taskbar thing wastes space when all it displays is a button called 'gadgets'
If you keep your files organized then there will be no need to use a desktop search engine.

-HellFire