Craigslist is actually the best bet. Ebay isn't as good, but it's decent if you live in smaller town or your town doesn't have a very active craigslist community. In the last 3 weeks, I've bought 4 Vita packages (systems + games + accessories), and I've sold 3 of those 4, so I can give some pretty good advice.
1. If you're going to buy a Vita, go all in on the Vita, and save big. What I mean by this, is that the more stuff you buy, the bigger discount you'll end up getting. You know you're going to want to play a bunch of games for it, and you know you're going to need some kind of memory card, and you're also likely to need some case. So, go ahead and buy a big bundle that includes all of it. You'll be able to save the most money that way.
The key is, list out everything that is included in the bundle, and next to it, put down a dollar amount of what you're willing to pay for that item.
REMEMBER - be cheap... You need to think from a standpoint that if you were forced to sell that item, how much would somebody pay you for it, if you had to sell it and needed to sell it fast. You shouldn't offer any more than that, for what you're buying.
Here is how I break down Vita packages:
Vita hardware - $200 or less (has to include power and usb cables) I'm willing to pay $195 for a 3G and about $175 for a Wi-Fi
Vita games - I'm willing to pay as much as $18 for games that I really, really want. If it's one of the Vita games that I'm not interested, then probably only $14, because I'll be trying to sell it or trade it.
Memory cards - 9 bucks for the 4 gig, 18 bucks for the 8 gig, 35 bucks for the 16 gig (I never see this one in the wild) and 55 bucks for the 32 gig. Trust me, don't pay more than that for the memory cards or you'll regret it.
Cases - Basically I would consider a case as 5 bucks, unless it's something really nice. One of my Vita's came with a very nice travel case that retails for like $29.99 or something, so I actually counted that as being worth 10 bucks.
Screen protectors - honestly, I don't really consider this worth anything.
Games on Memory Card or PSN accounts - Not really worth anything. Who wants to earn trophies on somebody elses account?
Ok, so, lets say there is a guy that is selling a Vita package, and it's a 3G Vita, and it comes with 4 games (3 of them you want, 1 of them you don't), and it includes a 4 gig memory card and a small case. The guy is asking for $350 for everything.
3G Vita - - - - - - - - - - - $199
1st game you want - - - - - $18
2nd game you want - - - - -$18
3rd game you want - - - - - $18
game you don't want - - - - $14
4 gig memory card - - - - - - $9
hard case - - - - - - - - - - - $5
Grand Total --------------- $281
Now, do you offer the guy $281 ? NOPE. $281 is the MAXIMUM you'd pay for that stuff. You'd like to get everything a bit cheaper. Tell the guy you have 260 cash money, and you can come pick up the item right away.
Basically, the best advice I can give is to buy a big bundle of stuff, but buy it at a big discount. Make sure the guy has several games that you would actually buy yourself if you weren't getting them in the bundle. Don't settle for a bunch of crappy Vita games. Here is a list of Vita games that I can absolutely recommend to anybody:
Fifa Soccer
Uncharted
Wipeout
Hot Shots Golf
MLB 12 The Show
Rayman Origins
Unit 13
Virtua Tennis 4
There are other good games, but those seem to be some of the most solid launch games. (two of the best Vita games are download only)
I've also heard good things about:
Lumines
BlazBlue
Marvel Capcom
ModNation Racers
Ninja Gaiden
