Shades of Doon
I really love this series. The main characters, Veronica and MacKenna are likable and proactive and intelligent. I will admit I'm partial to MacKenna as I love how she references Broadway Musicals and exclaims, "Son of a Sondheim!" She's more snarky and light hearted than Veronica, but that's a good thing as they balance each other out. If you haven't read any of these book, the first on is DOON and the second is DESTINED FOR DOON. For me to stick with a series this long - it has to be good ;)
I interviewed Carey and Lorie on my blog last year. Here's the link if you're interested: Interview!
Speaking of series....any recommendations? What's your current favorite??