I would suggest Harbord which has recently had a name change to Freshwater and Curl Curl. They are only a 5 - 10 min bus ride north from Manly and the rents are a lot cheaper than Manly. Both locations are by the beach as well.
You can also catch the 139 bus to Manly (for the ferry etc...) or there is an express bus (E65)that takes you into the CBD within 30 - 40 minutes.
I would suggest using
http://www.realestate.com.au/cgi-bin/rsearch?s=nsw&t=ren&snf=rbs&a=sfand/or
http://www.domain.com.au/Public/ChooseRegions.aspx?mode=buy&state=NSWfor property searches