What kind of mods?
If you're looking for skins google minecraft skins
http://www.minecraftskins.com/ (found mine here)
If you're looking for texture packs google minecraft texture packs
minecraftdl.com (is alright)
planetminecraft.com (is the one I use the most)
and http://minecraftcustomizer.net (is actually pretty cool where you can customize certain parts of texture packs via multiple choices)
If you're looking for bukkit plugins: