I lived in SoCal for three years and miss In-n-Out. I've often thought about a day trip to AZ, NV or CA just to eat there and come back home.
There is one place around where I live that has a pretty good burger:
Phillip's Grocery - Holly Springs, MS
(541 East Van Dorn Avenue, 38635 - 662 252-4671) Opened in 1948, Phillip's Grocery received national acclaim in 1989 when USA TODAY named their burger in the Top 3 nationwide; this classic two-story building just off the railroad tracks was built in 1882; over the years it has operated as a prohibition saloon and a brothel; it has decidedly more family feel nowadays; closed Sunday; open Monday 9 am - 3pm; Tuesday - Saturday from 9 am to 6 pm; try the fried apple or peach pie for dessert; highly recommended; check out the old railroad depot across the street. Phillip's Grocery has another location in Oxford at 2406 South Lamar Boulevard (662 236-5951).