Here's a list of the parties standing in this election that won seats in 2005.
Labour Party
Conservative Party
Liberal Democrats
Scottish National Party
Plaid Cymru
Democratic Unionist Party
Sinn Féin
Social Democratic and Labour Party
Ulster Conservatives and Unionists
UKIP, Green and the BNP are the other 3 notable parties, but that's probably a bit much.
Maybe Labour, Conservative, Liberal Democrats, BNP, UKIP, Greens and then one option for the Wales/Sco/NI parties would be best? And an option for other?