What are the best sites to get uci and winboard engines from?

Help!

Shouldn't matter as long as your browser and anti-virus program are totally up-to-date, between both programs you should be warned prior to visiting any bogus or unsafe sites. There are also web browser add-ons and utilities that help you stay safe while you're on the internet.

If you know how to use search engines you shouldn't have any trouble finding any chess freeware online

Here's a couple of sites:

http://www.chessmosaic.com/ChessEngines1.html
http://www.superchessengine.com/engine_download.htm

The best place is probably each engine's homepage:

Stockfish:  http://www.stockfishchess.com/
Houdini:  http://www.cruxis.com/chess/houdini.htm
Critter:  http://critterchess.sourceforge.net/
Crafty:  http://www.craftychess.com/
Rybka: http://www.rybkachess.com/

Etc.,

As NimzoRoy said, just use Google.  There are hundreds and hundreds of available UCI and WinBoard engines out there, available to download.

Thank you so much for taking time and effort to post. This helps a lot.