Wow. Thanks for the detailed response.
I actually will have a rental as well.
Oh, well, that opens up nearly limitless possibilities. But you'll need to go into this with a different mindset than a WDW vacation. At WDW people tend to brag how they "never leave property" for a week or more. Chuck that boast out the window in SoCal. Disneyland is a compact two-park resort property stuffed full of nearly as many rides and shows as all of WDW has in their sprawling four park property.
But there's a whole world of attractions beyond Anaheim in the greater SoCal area. If you are really just wanting something to do for a few hours after 6:00PM, you'll probably stick with Orange County proper. In September the sun sets at 7:15PM at the start of the month and 6:45PM at the end of the month. You should/could drive down the coast on PCH from Newport Beach to Laguna Beach in late afternoon, watch the sun set in Laguna at Heisler Park, and then have dinner somewhere in that artsy/ritzy beach town.
http://www.lagunabeachinfo.org/
If you want nightclubs or bars with the beautiful OC people, Newport and Corona Del Mar are the place to go in the evenings. The Shark Club is a trendy adult spot about 15 minutes down the freeway from Disneyland
http://www.sharkclub.com/ Or the Landmark Steak House is another good restaurant that turns into a piano bar/dance club after 10:00 PM
http://www.landmarknewport.com/ Be warned however, you are venturing into the heart of Orange County here in all its botoxed, laser resurfaced, pumped up, perfectly coiffed and perfectly attired glory. A TGIFridays in Cincinnati, this is not! It can be fun to ogle the locals and giggle a bit at their self-absorbtion though. It's like being an extra on a reality TV show.
Speaking of self-absorbed, OC has many great malls, but two in particular that are world famous. South Coast Plaza is a mega-mall with every famous boutique and designer in the world; Versace, Hugo Boss, Armani, etc., etc. all have big flagship stores there. It's about 15 minutes south of Disneyland.
http://www.southcoastplaza.com/ Then there's Fashion Island, which has many of the same very expensive stores and restaurants, but has the bonus of being on the ocean in a very attractive setting. It's about 25 minutes from Disneyland.
http://www.shopfashionisland.com/
If traditional malls aren't your scene, there's the Irvine Spectrum with is sort of a massive outdoor entertainment mall much bigger than Downtown Disney Anaheim, and even larger than Downtown Disney Orlando or CityWalk. About 15 minutes south of Disneyland and very heavily tilted to dozens of restaurants and clubs.
http://www.shopirvinespectrumcenter.com/
Now, if you are up for it, you could venture up to LA after 6:30PM and not have much traffic. A fun thing to do at night is visit Griffith Observatory in the Hollywood Hills. You'll not only have that famous sparkling view of Los Angeles, but you can look through the telescopes at Mars or the Moon. It's really a gorgeous facility, especially at night. It's open until 10:00PM nightly, but is closed Mondays.
http://www.griffithobs.org/
On your drive to or from Griffith Observatory, you could do a drive by of the Walt Disney Studios in Burbank.
http://studioservices.go.com/disneystudios/index.html
Another Disney connection is the fabulously restored El Capitan Theater in Hollywood. It's directly across the street from the Hollywood & Highland Center and the Kodak Theater where The Oscars take place each year. The El Capitan is a gorgeous old 1920's theater that is now owned by Disney and shows Disney movies exclusively. Before the movie they have a live organist play a concert, and on weekends they do a song and dance routine before the movie starts. Attached to the theater is Disney's Soda Fountain, an old fashioned soda fountain themed to Mickey Mouse. Check the website for show times and performances, as things change there regularly. On a weekday night you may not get the full song and dance treatment of the weekends, but it's an amazing place to see a Disney movie. Truly a one of a kind, only in Hollywood kind of a thing.
http://disney.go.com/disneypictures/el_capitan/index.html
The soda fountain and Disney Company Store is open later even on weekdays.
http://disney.go.com/disneypictures/el_capitan/soda_fountain/main.html
The El Capitan is about a block away from Grauman's Chinese Theater, where you can put your hands in all the old stars hand and foot prints.
http://www.manntheatres.com/chinese/
If you are museum fans, there's also some great stuff in LA proper. Of course there's the stunning and one of a kind The Getty
http://www.getty.edu/visit/
The Petersen Automotive Museum is one of the finest in the world, and really plays up its roots with SoCal Car Culture.
http://www.petersen.org/ And then the usual big city modern art and historical museums
http://www.lacma.org/info/HoursDirections.aspx
You might also like to visit the famous Walt Disney Concert Hall at the Music Center in downtown LA. Even if you aren't attending an event they have a hip gift shop and a great restaurant attached off the street. You can check performances for the Philharmonic, and there's also the Roy and Edna Disney Calarts theater (REDCAT) on the backside that has funky showings and performances most nights.
http://www.laphil.com/ http://www.calarts.edu/redcat
If you are looking for a day trip, I highly recommend Palm Springs, about 90 minutes drive east of Disneyland. The aerial tram there is spectacular, and you'll get an amazing ride from the hot desert floor up to the cool mountain top.
http://www.pstramway.com/ There's restaurants and a bar and hiking trails at the top, and Palm Springs is full of excellent shopping and dining and architectural tours.
http://www.palm-springs.org/
These suggestions are from a locals perspective, and they are in addition to all of the usual cliche' tourist activities like the Hollywood Walk of Fame, concerts at Hollywood Bowl, Santa Monica, Malibu, The Sunset Strip, Rodeo Drive, Mai-Tai's at Trader Vics at the Beverly Hilton, etc. (Okay, that last one is more my speed, but I recommend tourists try it too.)