Unfortunately

Unfortunately
 

Unfortunately I will not be able to attend the conference today.
Desafortunadamente (o desgraciadamente:erm:) no puedo asistir la conferencia hoy.

No siento cómodo usar la palabra desgraciadamente. ¿Se la puede
usar en este sentido? Su cognado en inglés disgraciously/disgrace conota
algo de vergüenza.

I don't know whether this might help:

unfortunatelyadverb

1 (unluckily, regrettably) (independent) lamentablemente, desafortunadamente; (stronger) desgraciadamente, por desgracia


2 (inappropriately): it was unfortunately worded estaba expresado de una manera desacertada or desafortunada

"Desafortunadamente" está bien en esa frase.

If you use "desgraciadamente" or "por desgracia" it looks it is sort of a tragedy not being able to be there. Of course, it'd be taken as a formalized and demure way to say "Oh, darn! I hate I can't be there, man!", so it's sort of a free pass to get emotional about 0.8 in Richter's scale.

"Desafortunadamente no podré asistir hoy a la conferencia." (or "a la conferencia de hoy", especially when there are more than one scheduled) it's a pretty neutral way to say it which still communicates genuine discomfort for not being able to attend.

Just a correction and an addition. :)

Thanks all for the info and correction. Lamentablemente sounds like a
more graceful word than desafortunadadamente. Now I know that
una degracia is a truly serious misfortune.

I would use "lamentablemente" (although "desgraciadamente" is also correct). ;)