Ive alwys liked Amistart, which is hugely configurable. Can be used as a dock, or a taskbar, or a combination of the two. I also like how you can have sub-docks (ie, extra dock items that run off of a single dock "entry"). You can also set some nice eye candy effects with it (transparencies and so on). The main two problems with it though is that it can be quite heavy on resources, and its a pain to initially get running (although once you get a working config, its easy to edit it with simple drop and drag, menus, and so on).
WB2000 is also quite nice, but like Amistart, a pain to initially get working.
