Like Johnboy said, SNA is a smaller airport about 35 miles south of LAX (you will have an EXTREMELY short flight of probably 15-20 minutes or so). The airport is actually VERY busy with a lot of private planes in addition to the commercial traffic. Many airlines serve John Wayne Airport (all US majors - American, United, Delta, Alaska, Southwest, Northwest, TWA, US Airways, Continental, and America West). The largest plane flown into SNA is the 757. You'll see many of those (especially AA and UAL). There are also quite a few 737s, MD-80/90s, and A320s. They actually serve many East Coast cities non-stop from SNA, including ATL, JFK, EWR, and PIT, as well as ORD, DTW, MSP, and DFW. It is a nice alternative to LAX.
I've been there quite a few times. The terminal is new (1992 or so), and it is one of the nicest I've been in (reminds me of Delta's terminal 5 at LAX). Lots of marble and palm trees. The best place for spotting is between gates 7 and 8. There is an indoor observation area. Also, go up to the top of parking garage on either side of the airline check-in counters for a good view of the traffic coming in and out.
It's too bad you're doing the commuter flight to LAX, because a take-off from SNA in a jet (especially a 757) is a treat. Due to the noise restrictions, the planes power full forward at a VERY steep angle on take-off, so it feels like you are being launched. Then, about 30 seconds later, they cut the power back to reduce noise for the neighborhoods below. It gives you an odd sensation of partial weightlessness/falling!! When I've flown AA out of SNA, the pilots always warn the passengers about this before take-off, so people don't get scared and think they are crashing. It is quite an experience!!!!
Hope this helps!