Some of the more popular universal tartans are:

Royal Stewart
Hunting Stewart
Black Stewart
Black watch (Campbell modern)
Pride of Scotland
Caledonia
Jacobite


All of these tartans are worn without regard to Clan affliation or surname.

A few common Clan tartans are:
Buchanan
Dress Gordon (White)
Gordon Modern (Military - Green)
Lindsay Modern
MacKenzie
MacLeod (Hunting - Green, official tartan of the Boy Scouts)
Wallace (Dress-red)
Wallace (Hunting-green)

These tartans are clan tartans but are worn by many individuals who want a kilt to wear around the house or to non-Scottish events. However, if you are attending a Scottish event, and do not have a clan it is best to wear a universal tartan.

All solid color kilts (non-tartan) are also worn without regard to clan or surname, but saffron and green kilts are associated with the Irish community in the minds of many people. Solid black is the most common choice for a non-tartan kilt. However, for those of Scots background a proper kilt should be made of tartan fabric.

Hope this helps. Good luck!