i use qualendar for calendar and todo and find it really good, it will probably improve with time too, loads of people prefer Kopi/Korganiser but it wasn\'t quite snappy enough for me, i prefer qualendar (and would like to take this opportunity to thank its author - if he ever reads this :-)) its free also...
For addresses I have tkcaddressbook (leftover from my 5500 tkcBundle) which runs fine as the addressbook, i like it more than the others (esp. as it uses the old XML format) even though I wouldnt buy any more software from them since they wont upgrade my 5500 versions to the 7x0 version. I find that only tkcAddressBook and tkcJabber were worth the money, explorer was great until Tree!ExplorerQt and most of the rest of the software i bought is redundant on the the ROMs. tkcAddressbook could also be better, but i wont hold my breath.