You should check out a few things:
LinqToOracle at CodePlex
http://linqtooracle.codeplex.com/
Supposedly there is some .NET 4.0 beta related activity going on. [Update: "Supposedly" looks to actually have meant "Not at all."]
Another similar SO question
http://stackoverflow.com/questions/30790/is-there-a-way-to-use-linq-to-oracle
A bit dated, but a decent place to start.
DevArt's dotConnect for Oracle
http://www.devart.com/dotconnect/oracle/
They've got a free trial. Was previously known as OraDirect.
Personally, I've kinda given up on this myself, content to wait for support in the Oracle data provider from Oracle.
[Update]
Oracle's ODP.NET
http://www.oracle.com/technetwork/topics/dotnet/whatsnew/oracle-entity-framework-sod-130214.pdf
Oracle's own data provider will support it in 2011, with a beta available near the end of 2010. Better late than never, eh?