As mentioned Benjamin Disraeli was a Sephardic Jew by ancestry and culture, although he converted to Christianity relatively early in his life. I even think that he embraced his Jewishness to some extent. Responding to an anti-Semitic attack against him in the House he replied "While the honourable members ancestors were living in leather tents on a foggy island falling off the edge of the world mine were building the temple of Solomon." He was later made the Earl of Beaconsfield. His last words might have been the Shema. Lionel de Rothschild was an MP but had huge troubles taking his seat because he refused to take the oath which required him to swear “and I make this Declaration upon the true Faith of a Christian”. Eventually a Jews Relief Act was passed to allow him to keep his seat but the House of Lords blocked it for over 10 years before it was made law. Gladstone even proposed to Queen Victoria that he be made a peer. She demurred, saying that titling a Jew would raise antagonism and furthermore it would be unseemly to reward a man whose vast wealth was based on what she called "a species of gambling" rather than legitimate trade. She did however elevate his son Nathan to the peerage in 1885. He was the first Jewish member of the Lords.

http://www.yivoencyclopedia.org/article.aspx/Ezofowicz_Family

There was a family of rich Jewish businessmen in Lithuania, Jan Abraham Ezofowicz converted to orthodox christianity and was made a noble in 1507. This wasn't particulary rare - there were a lot of such people.

More interestingly - his brother Michał (in other sources - Meira) Ezofowicz haven't converted, but was also ennobled (with his kids and so on) in 1525.

They both held important offices, including tax collection, toll bureau, and even the main Lithuanian council.

Michal Ezofowicz and his descendants are the only examples on record of Polish [should be Polish-Lithuanian, or just Lithuanian] Jews who achieved noble status without conversion. They are the subject of Eliza Orzeszkowa’s novel Meir Ezofowicz.

There were no degrees of nobility - each noble had equal rights, including election of kings.

I don't know whether this is the kind of answer you were looking for, but in order to give you another example... the Pierleonis are a noble family whose ancestor happened to be a Roman Jew who had converted to Christianity sometime in the 10th century AD, and was later granted a title by Pope himself. The family was quite prominent in Rome during the Middle Ages and not only many of its members were made cardinals, but the House itself can also boast an anti-Pope among its ancestors (that'd be Anacletus II, 'reigned' 1130-37).