I'm a huge fan of OmniPlan for my development planning. It lets me set up my tasks, gantt chart them, measure resources, get a rough idea of how long things are going to take, and it's very friendly and interactive.
Unfortunately it appears that people like BaseCamp and FogBugz have a religious dislike for gantt charts. They can certainly be mis-used, especially if you let the document become the project, instead of documenting the project. For me, OmniPlan's implementation lets me easily put into the tasks, assign who's going to do it, make estimates, put in work-weeks, and then automatically see when things will get done. The utility of the estimate is obviously dependent on my ability to estimate.
Now my client would like to know if there's any online / hosted type tools with the same capabilities. Since OmniPlan is Mac only... are there viable alternatives?
(And no, I'm not going to give up on gantt!)
This could be a starting point: http://pm-sherpa.com/features/basecamp-alternatives/ There are 45 alternatives to BaseCamp there and counting. It's strange... Who knows how many competitors exist (and survive) due to BaseCamp's refusal to make a danged Gantt chart. 37signal's systematic dismissal of the massive and continuous customer demands for Gantt charts made me get off the 37signals fanboy train. I think if they listened just a wee bit more to their customers instead of to themselves, they would not have 45 competitors.
You might want to have a look at Easy Projects - http://www.easyprojects.net.
It includes a lot more features than stripped down project management apps such as Basecamp and therefore takes a bit more getting used to but does include Gantt charts.
I use Easy Projects quite regularly and have used Basecamp, Huddle and Pelotonics in the past. I like the way that apps such as Basecamp are really simple and quick to use but I also like the greater functionality offered by Easy Projects for more involved projects.
Hope that helps.