All of Lisa's series books stand alone...
...but if you're interested in reading them in order, here's a handy list for you!
"Perfect" series
Perfect Together (2003)
Perfect Switch (2004)
Kismet Christmas series *
Home for the Holidays (2008)
Holiday Affair (2010)
Together for Christmas (2012)
Morrow Creek series
The Matchmaker (2003)
The Scoundrel (2006)
The Rascal (2006)
"Marriage at Morrow Creek" in the anthology Hallowe'en Husbands (2008)
Mail-Order Groom (2010)
The Bride Raffle (2011)
Wanton in the West (short-story/e-book exclusive) (2011)
"Something Borrowed, Something True" in the anthology Weddings Under a Western Sky (2012)
The Honor-Bound Gambler (2013)
You can also visit Lisa's RomanceWiki page to view a list of books in the "Perfect," Kismet Christmas, and Morrow Creek series in reverse order (most recently published first).
*Note: So Irresistible is a prequel to Together for Christmas, but is not part of the Kismet Christmas series.