I would be strongly biased towards purchasing Myself, Yourself ... I liked the series a lot, particularly the opening theme which I bought the single for the last time I was in Japan
Other series, anything ToHeart/ToHeart2 related ... I have your release of series 1 and the Japanese releases of everything else (and the upcoming OVA due later this year on pre-order) but I would quite happily double dip on all of it. Ef, both series, would be a nice couple of series to have along with KimiKiss Pure Rouge and the various Minami-ke installments.
The two series though which I think would fit well with you previous releases would be Manabi Straight (in a Gakuen Alice sort of way) which is a nice school based series about people working together to achieve something against the odds and Aoi Hana (a summer '09 release currently available via CrunchyRoll), which looks to be a nice gentle series with a, slightly more yuri, Maria-sama feel.
Speaking of which, any chance of talking to someone like Yen press and trying to get the Maria-sama manga/novels released in English?
edit: looking back at the previous postings I think I should make clear for the record that whilst I like to have a dub available, if possible, to give me the option of watching a series that way I actually tend to watch things normally subbed anyway so a release which is not dubbed is not a show stopper for me (and I understand some of the reasons why you may not want/be able to justify a dub track for every series)