Ask HN: What services do you use for tasks and contacts?

I am the co-founder of the start-up komola UG ( http://komola.de ) and am trying to find some more ideas for our upcoming Software-as-a-Service suplify ( http://suplify.me ). We want to make support software mainly which uses all streams from which support requests come being email, twitter, facebook and many more. But out product will also feature a section where we try to aggregate the customers contact data and have a list of tasks. Because we think that this information (contact & tasks) should be synced with other services I am trying to make a list of the most popular services so we can integrate them first.

For now here the list I made (the further up the more important):

_Contacts_ * Google Contacts * Highrise

_Tasks_ * Remember the Milk * Google Calendar / Google Tasks * Highrise

I would appreciate your help! Thomas (This is my first post here after lurking for about 9 months)