I'm not sure, but Mint.com seems like a good place to look for ideas. They have somehow persuaded me and millions of others to hand over all our banking passwords.
Gaining this trust, though, will probably not be easy. One advantage a site like Mint has is that they have so much content and so many partnerships that it is clear they are not a scam, have enough at stake to not misuse my information, and probably have the resources to keep it safe. A site like yours, however, could easily have been cobbled together in a number of hours by a scammer. (I don't mean this as a criticism -- I actually like your site. It just doesn't have anything on it to suggest that you are the sort of business I can trust with my passwords.)
It helps at this point that Mint itself and its corporate owner Intuit have a long history of reasonably good online security (certainly better than some banks I've used), plus the whole "owned by Intuit" thing gives a solid paper-trail to keep anyone from recourselessly running away in the night with my information.
Gaining this trust, though, will probably not be easy. One advantage a site like Mint has is that they have so much content and so many partnerships that it is clear they are not a scam, have enough at stake to not misuse my information, and probably have the resources to keep it safe. A site like yours, however, could easily have been cobbled together in a number of hours by a scammer. (I don't mean this as a criticism -- I actually like your site. It just doesn't have anything on it to suggest that you are the sort of business I can trust with my passwords.)