Hi Barke, it's too bad our hosts' meddling moderators all but closed down the community forums here a while back -- five years ago you'd have had a dozen helpful expert opinions before last night was out. Hopefully they'll chime in in the next few days.
From a very inexpert point of view: the early-mid-'70s baseball have some collector value, '80s-'90s stuff generally less so. Pre-'80s cards of star players have some value, post-'80s generally little, except for rookie cards of those stars. When we say "some" value, we don't mean "a lot." It would be helpful (for you) if you had some knowledge of players in whichever sport, to help you idntify which cards might carry a premium. Since your husband (sympathies on your loss) was a dealer, it's a fair guess that the cards he kept in sleeves have more value than those he didn't.
Other guys on board here can tell you some specific cards to look for (rookie cards of Derek Jeter, Ken Griffey, Michael Jordan, &c'). Otherwise your best route would probably be putting them up for auction here somewhat as they're already grouped ("unopened box of 1976 Topps baseball," "unopened box of 1989 Collector's Choice Premier Edition," "assortment of LeBron James cards," &c'), and "letting the market decide."
Anything that doesn't sell at even a low price can be donated to a youth sports league, AmVets, Goodwill, or another charity or good cause.
