The best things for me right after having kids were getting uninterrupted shower time (daily--I almost never shower daily now, but right after having kids it was totally needed), not having to cook dinner every night, and getting a nap in even if the baby was NOT sleeping. Later I really appreciated getting to work out regularly and usually did it with my infant in the bouncer while my toddler slept. I'm also expecting #3 and haven't been able to work out around my kids safely for some time and find that most mornings I want sleep more than I want exercise.
Going for a walk without a stroller would be great. That doesn't take long, you can go quickly, swing your arms, and look around you.
Reading in the tub without having to hear "Mommy, where are you???" or "Are you coming down soon?"
Meet a friend for coffee before the kids wake up once in a while. I meet a friend one morning a month. I am fried by the end of the day (we meet at 6:45 and I normally don't get up for work until 7:15) but it is totally worth it to see another grown-up alone.