Here are the current Justices:

• William H. Rehnquist. Before being appointed by President Nixon, he was active in Republican politics. One of two appointees in 1971, the other belonging to Lewis F. Powell. Rehnquist is a member of the conservative bloc, and also replaced a conservative, John M. Harlan, who nonetheless often sided with the liberal majority on civil rights cases.
• John Paul Stevens. Originally seen as a moderate, independent justice when appointed by President Ford, he has come to be seen as a very liberal justice in more recent years. Although, this perception may be accentuated by the fact that many of his colleagues were replaced by much more conservative Justices. Stevens is not one for forging consensus and often authors his own opinions. Liberal groups that were originally opposed to his appointment have since become his biggest supporters. Justice Stevens replaced William O. Douglas, a much more activist Justice with a strong human rights interest.
• Sandra Day O'Connor. Appointed by Reagan, she was a Republican State Senator for Arizona earlier in her career. While not activist, she is not a member of the conservative bloc either. With some conservative tendencies aside from sexual discrimination cases, she is often a swing vote. She replaced another centrist, Potter Stewart, who nonetheless would probably have been seen as a liberal on today's court.
• Antonin Scalia. Appointed by Reagan, he filled the opening left by Warren E. Burger when Rehnquist replaced the retiring Burger as Chief Justice. Scalia is outspokenly conservative, a strict constructionist, defers to states rights, and refuses to judge whether a law is an unwise or bad law - only whether it is constitutional. His legal reasoning has been criticized as inconsistent when consistency would lead to an opinion misaligned with the political right. His predecessor Burger was a centrist and not a member of the conservative bloc.
• Anthony McLeod Kennedy. Appointed by Reagan after the unsuccessful nominations of Robert Bork and Douglas Ginsburg. Originally seen as conservative, he has come to be seen as a centrist, and as seen as part of the "centrist bloc", similar to O'Connor. However, his style is significantly more conservative than previous Court generations. He replaced another then-centrist, Lewis F. Powell, Jr., who was appointed the same year as Rehnquist (1971), replacing Hugo L. Black, who was a very liberal/activist Justice.
• David Hacket Souter. His appointment by President Bush was intended to strengthen the conservative bloc. However, he ended up being a key swing vote, aligned with the centrist bloc of O'Connor and Kennedy. His appointment is seen as a miscalculation by President Bush, and his tendencies are to not undo the precedents set by the liberal courts before him. He replaced William Brennan, who was seen as a liberal.
• Clarence Thomas. His appointment by President Bush led to what is probably the widest ideological swing from one appointment in recent history. Active in Republican politics earlier in his career, including an effort to mute federal affirmative action guidelines, he replaced Thurgood Marshall, a liberal activist black justice who was extremely active in civil rights. Thomas has become part of the court's conservative bloc with Scalia and Rehnquist. The confirmation vote was extremely close due to allegations he sexually harrassed a coworker, and the controvery surrounding the 98% male Senate voting on sexual harrassment led to a strong movement of women congressional candidates in later years.
• Ruth Bader Ginsburg. Appointed by President Clinton, her career was forged mostly on several important sex discriminations cases that she argued before the Supreme Court. Seen as a liberal, she nonetheless expresses some conservative views and aligns herself with the belief that the Court should not overturn bad laws; only unconstitutional laws. She succeeded Byron Raymond White, who was a pro-civil-rights Justice but conservative otherwise. Ginsburg's appointment is seen as a moderate shift to the left overall.
• Stephen Breyer. Appointed by President Clinton, he replaced Harry Blackmun, who was originally seen as conservative but came to be seen as one of the most activist libertarian Justices after the abortion cases of 1973. Breyer is a financial and antitrust expert and is seen as an "intellectual counterweight" to Scalia. While supported strongly by Democrats, his was not a controversial appointment.

Interesting statistics:

• Nixon(R) had three appointees with a four-year term, one of which is still active.
• Ford(R) has one appointee in four years.
• Carter(D) had zero appointees in four years.
• Regan(R) had three appointees in eight years.
• Bush(R) had two appointees in four years.
• Clinton(D) had two appointees in eight years.

That seems pretty skewed. For the last seven justices, democrats and republicans have been in power twelve years apiece, and yet (R) has five justices, (D) has two. Why?

Also you can see where the largest shifts in judicial belief were.

• Black->Powell->Kennedy was a clear move from liberal to centrist.
• Burger->Scalia was a clear move from centrist to conservative.
• Brennan->Souter was a move from liberal to centrist, while Bush's intention was for the shift to be more dramatic.
• Marshall->Thomas was about as dramatic a shift as could be imagined. A similarly dramatic shift in the opposite direction seems impossible.
• White->Ginsburg is a shift from moderate right to moderate left.
• Blackmun->Breyer is a shift from activist left to moderate left.

In terms of collective philosophy, Clinton's appointments probably actually resulted in a slight shift to the right, given how activist Blackmun was. However, there are now two left-leaning justices where there was one very activist judge, so it's actually a net shift to the left.

President Bush's appointments were by far the most aggressive in intent. I wonder if that is hereditary. One can also see the effect of 12 years of uninterrupted power by one party - both Justices he replaced were liberals, both resigning earlier in his term. Both were probably trying to outwait a Republican administration.

This is all relevant when trying to predict how the Supreme Court justices will act in future years - the general expectation is that at least one Justice will retire during this four-year term of President Bush.

While O'Connor is seen as a centrist, it's known that she was outspoken about not wanting to retire while Clinton was in office, due to her Republican history. Her politics can be seen as risk of another shift to the right.

Scalia has expressed dissatisfaction with being a Justice, due to not enough decisions going his way, but would probably not leave while a Democrat is in office. He is probably going to wait out a couple more court shifts to see if the court makeup changes to something more to his liking.

One has to wonder why Stevens did not retire while Clinton was in office. If Stevens retires while Bush is in office, we could see another dramatic ideological shift for the Court.

Rehnquist is seen as a likely retiree while Bush is in office. There's an opportunity for the Court to move slightly to the left if Bush is unable to appoint someone as strongly conservative as Rehnquist.

Finally, it is rumored that Ruth Bader Ginsburg is in poor health. This opens up another possibility for a shift to the right.

Thomas, Kennedy, Souter, and Breyer are all young and will probably be part of the Court for many years to come.