In case you don’t want to throw down $4.99 for the official Craigslist app (which is awesome BTW) you can get SearchCraig free from Volcari Software. It is not as full featured as the official app but it gets the basics done with elegant simplicity. They recently updated their Craigslist search app to v2.13 with some small improvements.
The app simply lets you search Craigslist easily from your BlackBerry. So far it only supports US Craigslist sites but it lets you search all main categories except for forums and personals. You can also easily reply to posting through email from your BlackBerry.
You can find SearchCraig free in the store at this link. Kudos to Tashanna for pointing this one out!