well freesteam.org is also good,i got kermis weapon packes from there,sensor tool,alot cool maps,connas tool pack/(cool one i recomend ,you can do cool things whitout wire,it can make npc animate,model manipulator,rotate tools ,sensor tools)
easyer and faster way is use svn links (http://wiki.garrysmod.com/?title=SVN_Links#Wire_Mod_2) ,i use tourtoise svn for that.whit svn you can download wire,stargate and other packs like that whit only 5 MINUTES,you dont even have to extract those files.