I don't really think approval ratings are that important since the public seems to change opinions with almost every decision a president makes. On lists of the highest approval ratings and lowest approval ratings on record, both Bushes and Truman are on both lists. I believe that Kennedy is the only president whose rating never went below 50%, but that may have changed if he'd lived longer.
Date Organization Approve Disapprove No Opinion Sample Size
5/29-31/09 Gallup/USA 61 34 5 1015
5/26-6/1/09 Quinnipiac University 59 31 10 3097
5/17-20/09 Amer. Res. Group 61 32 7 1100
5/14-17/09 CNN 62 35 3 1010
5/12-13/098 Fox/OpinDynamics 60 30 9 900
5/10-12/09 Democracy Corps 59 33 8 1000
5/6-12/09 CBS 63 26 11 1874
4/23-26/09 NBC/WSJ 61 30 9 1005
4/23-26/09 CNN 63 33 5 2019
4/22-26/09 CBS/NYT 68 23 9 973
4/22-23/09 Fox/OpinDynamics 62 29 8 900
4/21-27/09 Quinnipiac University 58 30 12 2041
4/21-24/09 ABC/WP 69 26 4 1072
4/17-20/09 Amer. Res. Group 57 38 5 1100
4/14-21/09 Pew 63 26 11 1507
Compared to Past Presidential Performance
President Highest Lowest
Obama 76% 2/7-8/09, CNN Poll 55% 1/26-29/09, Democracy Corps Poll
Bush (G.W.) 92 10/8-9/01, ABC News 19 2/16-19/08, Amer. Res. Group
Clinton 73 1/28/98 NYTimes Poll 36 5/26-27/93, Yank/Time/CNN Poll
Bush (G.H.W.) 89 2/28/-3/3/91, Gallup Poll 29 7/31-8/2/92, Gallup Poll
Reagan 68 5/8-11/81, Gallup Poll 35 1/28-31/83, Gallup Poll
Carter 75 3/18-21/77, Gallup Poll 28 6/29-7/2/79, Gallup Poll
Ford 74 8/16-19/74, Gallup Poll 37 1/10-13/75, Gallup Poll
Nixon 67 11/12-17/69, Gallup Poll 23 1/4-7/74, Gallup Poll
Johnson 80 2/28-3/5/64, Gallup Poll 35 8/7-12/68, Gallup Poll
Kennedy 80 3/8-13/62, Gallup Poll 56 9/12-17/63, Gallup Poll
Eisenhower 79 12/14-19/56, Gallup Poll 48 3/27-4/1/58, Gallup Poll
Truman 87 6/1-5/45, Gallup Poll 22 2/9-14/52, Gallup Poll
Roosevelt 84 1/8-13/42, Gallup Poll 48 8/18-24/39, Gallup Poll
Sorry I'm so lousy at formating.