If you're doing development against an Oracle database, you can use the built in Oracle client, System.Data.OracleClient. However this is a bad idea for a two reasons:
Hey Rad, how would i use LINQ when developing against an Oracle database???
Since Oracle are deafeningly silent on the matter, currently the best way is to use a third party provider. I keep hearing good things about Devart dotConnect. You could also check out the open source dbLinq or LinqToOracle
Thanks for pointing out that Stephen, I had overlooked it on that perspective and always compared LINQ to other ORM frameworks which always seem to have a common defacto - support for multiple db platforms. I guess IBATIS in combi with Abator.NET would achieve the cross-db-platform ability.
Thanks guys this is usually a big challenge when developing a site that may need to support different data stores.