I'm in the same boat as you. We thought we were done and got rid of everything between 2 and 3, and now, I'm two weeks out from our induction date with #3. I have purchased some stuff, borrowed a TON from friends, and gotten some things off Craigslist/freecycle/a mom's list serv I'm on. Start asking around - it's amazing how many people haven't parted with their baby stuff yet.
This go round, we got a Joovy Kooper stroller, a bumbo, a rock n play (they didn't have this with my last kids - looks like it could be a nice soothing containment device), and a bouncer from one person who was moving and another who let me shop her basement. The handy thing about the basement friend is that she's saving stuff for another friend, so when I'm done, I can give it all back to her. Another friend gave us her crib and changing table/dresser. I bought an Ubi stainless steel diaper pail from Bloomingdales during a great sale.
My next door neighbor turned out to have a stash of 70 Bum Genius 4.0 diapers that were in excellent shape...that she gave to me. Score!
Neither of my kids used a playmat so I didn't try to acquire one.
Baby swing - I got one at Target for 70% off, which was less than what people were asking on Craigslist. Target has had some awesome baby bargains in the past 6 months, so definitely keep an eye out there for deals.
Infant seat - we skipped this with our 2nd and are skipping it with our 3rd as well (going straight to convertible).
I did buy some Aden & Anais swaddlers (the big ones) this time and they are so soft. I got a new Miracle Blanket, bought bottles because my kids want to try and feed the baby, and we made a wooden cosleeper modeled after the $350 one I spotted at a trendy baby site.
For toys, I tried to have less! We now have a Sophie, a Winkle, and a Lamaze Mortimer the Moose, which were our favorite toys with the other kids. A friend gave me some Haba wooden rattles, too.
I know my list seems huge, but this is SO much less than we had with the other kids, and we spent FAR less, too.
Mama to miracles, dd (3/09), ds (12/10), dd (8/14)