There have been some big droughts in reliable third basemen in my Cardinals fandom (which dates back to the early 80s), but there are three third basemen that can be said to be 3 key Cardinals 3B's. Each one were (or are) on great, successful, and memorable Cardinals teams.
I am of course leaving out Todd Zeile, but his teams were not nearly as memorable, although he was a decent enough player. The first memorable third baseman in my lifetime was Terry Pendleton. While Terry's prime was not until he was on the Braves, he did put up over 4 fWAR once for the Cardinals, and his next best was just under 3. While a Cardinal he was part of some elite defense, and was always known as an above average defender. His offense was also a tick above average, so he was an all around player... just not a flashy all around player.
Pendleton's height of power with the Cardinals was in the NL Pennant Champions year of 1987: .336 wOBA, 96 RBI, and 19 SB. Terry's weakness were that he was a low power third baseman and his OBP peaked out at .360 and was usually much lower than that. Still, he was a player most teams would want and he had some decent speed. Perhaps the most interesting thing about Terry Pendleton is that his peak was around age 30, when he had moved on to the Braves. As a Cardinal, Terry had nearly 15 fWAR between '84 and '90.
The Scott Rolen era was short and sweet. 5 years of amazing production (one season was injury shortened quite a bit though in '05). Rolen peaked a bit sooner than Pendleton, and it was much, much higher: in 2003 Rolen went ahead and put up 6.7 fWAR which meant .390 wOBA with plus defense. The next season he outdid himself and had historic production levels of 9.2 fWAR, .421 wOBA, with elite level defense (not to mention, 34 HR).
2006, after coming back from a major injury, Rolen was more at his average offensive pace, but still with amazing defense, one of the greatest 3B in the league. He just wasn't quite as extraordinary after that injury. In just Rolen's time in StL, he amassed over 26 fWAR. Scott is still playing and has almost passed 75 fWAR for his career. In Scott Rolen's final year as a Cardinal, his defense was still elite but his hitting had fallen off, and he ended up being traded away after a truly spectacular run. One of the only great hitters whose defense outshined his superb hitting.
And bringing us to the present, David Freese has been something of a mix of Rolen and Pendleton. He is probably much closer to Pendleton than Rolen, but he is yet another different type of player. The first thing you'll notice from this series of graphs presented here is that David Freese got quite a late start to his career, an atypical MLB career so far for sure.
Starting at age 26, Freese's on-base percentage has been closer to pre-28 year old Rolen. If I were to guess, it looks like Freese will peak next season like Pendleton did when he hit 30. He of course won't get near Rolen peak offensive production (which is not surprising!), but he should be able to easily out-do Pendleton peak production, at least OBP-wise. Next is the graph for an even more rudimentary stat:
Here we see that Freese's offensive production is much more of a batting average fueled production, typical of many of the more recent Cardinals hitters. Another thing I notice so far from looking at these is just how up and down the careers of Pendleton and Rolen were/are. Freese looks to be a minimum .290-.300 BA hitter.
Next, we will see what could endanger David Freese's status as a high average hitter, and could also mess up his OBP of course:
David Freese's walks to strikeout numbers are pretty terrible. He is often very vulnerable to certain pitches like sliders, and if he doesn't correct this problem it could hurt him going forward. As you can see, he's not even that close to the average mark for 26 to 29 year old players. Granted Pendleton often wasn't much better, but he was at least average. This also illustrates Rolen's greatness as a hitter (beyond probably having more power). He was just far more disciplined in the art of hitting during his entire career except for his mid 30's years and probably onward. Freese does have a few more years to work more towards league average in this area, on the bright side.
And finally, here's a timeline showing the careers of these 3 third basemen using weighted on-base percentage (for those not aware of wOBA, it incorporates just about all forms of hitting skills and scales it to something similar to OBP... think better version of OPS). It is a great sign that Freese's wOBA is the best of his career thus far, and he may be still entering his prime even after already playing a key role in the world series championship last year.
It appears that this season Freese will finish around 4.5 fWAR, the highest in his career (one big factor is that he has played more this year). He's projected to finish above .360 wOBA, which is about where Terry Pendleton peaked at in his career. His defense has been above average and he has shown a great arm and knack for making one-handed plays into outs. It is also pretty likely he will hit 20 home runs this year, and that's about all anyone has ever wanted from the guy. So far, Freese has been worth over 8 fWAR as a Cardinal.