If you want to download wav sounds, i would like to give you the advice to add what kind of wav sounds you are looking for because wav files are used widely:
You can make some sounds effects yourself, for example, you own sound adventures
Or custumize you pc, make your own gsm ringtones...
Anyway have a look on this list if sites, that you'll find below:
http://www.findsounds.com/
A search engine with sounds in the format AIFF, AU and WAV.
stonewashed
an index of sites withs links to a database of sounds.
http://www.grsites.com/sounds/
a database of sounds.
And a base of sounds with a lot of ads :/ of sounds of famous marks of cars:
http://enginesounds.free.fr/