your main two choices on the mac are " omniplan" and " merlin2" @
www.projectwizards.net you'll have to select the english version of the site . [merlin is very involved and costs 225.00]
Omni plan is " project management made simple " and I think it was 149.00 when I bought it . I'd suggest you take a look at trial versions of both and see which " feels right " to you .