Similar meaning, but more neutral:
* Curiously
* Oddly
* Unusually
* Peculiarly
* Unexpectedly
More negative connotations:
* Weirdly
* Eerily
* Uncannily
* Mysteriously
* Suspiciously
More positive connotations:
* Intriguingly
* Remarkably
* Uniquely
More specific:
* Abnormally
* Bizarrely
* Inexplicably
* Unaccountably
The best word to use will depend on the specific situation and the tone you want to convey.