Ironically, the fact that the number of possible lifts is limited with just dumbells will actually help you; it will focus your training and cut out a lot of crap that would otherwise confuse and discourage you.
I prefer the dumbell press to barbell press because it requires more horizontal control (thus more muscles employed), plus no spotter is necessary. For similar reasons, the dumbell row is a quintessential back exercise in my routine. These two exercises are my two main upper body lifts, although I consider pullups and shoulder presses important as well.
Almost all the olympic-style lifts can be done with slight variations with a dumbell.
Shadowboxing with dumbells is always a fun and demanding exercise.
Plenty of exercises popularized in kettlebell routines can be applied to dumbells, though there are important exceptions.
Overall I think the humble dumbell is one the greatest, yet least appreciated, exercise tools to date.