Budget is upto £100 a night. Central ish.

Washington Suites in Georgetown, especially if you have family. If not it's still a great location with a good local bar 2 doors away and a 5 minute walk to the bars and restaurants of Georgetown, also handy for the bus and metro. Very safe area. Check it out on Google street view and walk down into Georgetown (sorry tried pasting the link but it didn't work).

Looks a nice place, unfortunately its £60 a night too expensive.

As you've been to DC, what is best to see? Some help filtering out stuff to do would be useful given the amount of attractions.

Surprised it came out that expensive, did you try expedia, travelocity or kayak?

Like most large cities you can't go wrong with the hop on/off tourist bus. A good walk is to start at the Lincoln Memorial then walk east passing the Vietnam memorial, reflection pool, monument, call in at the Smithsonian then keep going until you reach the Capitol.

Terrace bar at the Hotel Washington on 15th St NW gives good views of the area around the White House.

Georgetown has good bars and restaurants.

JW Marriott in central, near museums and White house. There isn't much in the city really all business places. Georgetown is nice but quite expensive.