Datebk is the best I've seen, but it's Palm. CESD has sent emails saying he is porting it to Windows as a desktop app, and i suppose we can dream it will also come to Linux, and then a Maemo port.
GPE contacts is ok, not perfect but I can live with it. I have no problems with memos, but there are some Palm memo replacement apps around. I haven't bothered. Integration is a fairly large deal. The ability to get to PIMs instantly is part of the zen of Palm. I'm still carrying my Lifedrive, and still prefer the T3, but the wifi hotsync and a few other things put that in a drawer. I see nothing at all for Maemo that rivals any Palm PIM app, but since I found pyring I'm close to giving up my Palm. PIMs aren't at the absolute top of my list. An acceptable password safe that can import Keyring files was holding me back, but pyring does that. It's not perfect, but it works well enough.