If people don't mind, I'll post my "things to do" list here, maybe someone wouldn't mind sharing their experience or dropping a tip or two.

I know Philadelphia is worth seeing, but I'm on a tight schedule, so I can't do much more than that. Also, all of these are just a plan - I'll do as much as I can, hopefully all, but if I can't make it, so be it. Most of the stuff doesn't take much time, because it's just coming to a place, taking a picture of it and moving on (especially in LA). San Francisco seems busy, but I'll be there from 1pm on 18th till around 4pm on 20th.

Please feel free to bash it if you'd like, I need to figure out the ideal "to-do" list, as the schedule is pretty tight and I need to keep up with it (I like it this way though).

THANKS for chipping in everyone!

NEW YORK CITY (buying City Pass - $89)
- Statue of Liberty, ferry [city pass]
- “Friends” building
- Empire State Building, skyline [city pass]
- Broadway
- Museum of Modern Art [city pass]
- Central Park
- Metropolitan Museum of Art [city pass]
- American Museum of Natural History
- Top of the Rock, Rockefeller Plaza [city pass]
- Times Square

PHILADELPHIA
- Philadelphia Museum of Art [$16]
- Try Chese Whiz
- Check out city center

WASHINGTON DC (going through all the National Mall)
- National Gallery of Art
- Lincoln Memorial
- National Museum of American History
- The White House
- The Capitol
- International Spy Museum [$20]

If there's enough time:
- Georgetown
- National Cathedral
- National Zoo Park
- Meridian Hill Park

GRAND CANYON
- Air Plane tour / Sunsent Jeep tour (depending on $)
- Some hiking, maybe a bus tour or rent a bicycle

LOS ANGELES
- Grauman’s Chinese Theatre
- Hollywood Boulevard
- Hollywood Sign
- Griffith Park
- Olvera Street
- Staples Center
- Venice Beach
- Third Street Promenade
- Westwood Memorial Park
- Rodeo Drive

If there's enough time
- Runyon canyon Park
- The Getty Center
- Universal Studios Theme Park/Studio Tour (depending on $)

SAN FRANCISCO (buying City Pass - $69)
- Cable car around the city
- Museum of Modern Art [city pass]
- Coit Tower
- Beat Museum
- Mama’s Diner
- Telegraph Hill steps
- Blue & Gold Fleet Cruise, incl. Alcatraz [city pass]
- Pacific Heights
- Exploratorium [city pass]
- Haight Street
- Twin Peaks Photo spot
- Golden Gate Park
- Golden Gate Bridge

If there's time
- AT&T Park
- San Francisco Bay Area
- Fine Arts Museum [$10]