First off, the lenses are fine for almost anywhere at IAH
As Bruce said, the parking garages at Terminal B are endorsed by the H.A.S. as a place to go and enjoy the sights. Same goes with the Terminal C and D garages as well. The better time of year to use these places is in the spring, fall and wintertime when the sun is behind you. There is a new parking garage that is nearing completion for Terminal E that has yet to be checked out by us locals so when that happens, we may have some more news to report. The thought is that during this time of year, the afternoon could work with a good telephoto lens (100-400 or 75-300mm type) as planes taxi in on the north east bridge between rwy 27 and the International Terminal. Stay tuned for that.
Another place which doesn't get too much notice is the Marriott Airport parking garage. Though it's pricey (5.00/hr), in the summertime evenings, you can get nice taxi shots of RJs and 737s, etc. at pretty close range, sun mainly on the nose but slightly in your favor. No ladder needed.
As for the outside places, with the new runway 8L
/26R in use, there are still new places to be explored. The H.A.S. has begun a program involving mounted rangers on horses patrolling the peremiter fences so there could still be some resistance to new places being found. By the way, has anyone here in Houston seen anyone actually using the horse trails?!
The Lee Rd. parking area is a favorite for nose on arriving planes this time of year, and during the wintertime, good to park and walk a bit down the road to shoot with the sun behind you. There is a great spot at the end of Rankin Rd. on the west side that is kind of open if you park your car and walk. There you can get nice afternoon takeoff shots, but officially, it's not exactly open. We here in Houston have been talking on and off again with the H.A.S. about reopening that parking spot, but nothing yet has come about.
Anyway, there are still a few places to shoot from at IAH
and with the new carriers we've picked up this year (PIA 777, SVA 742F, CAA A340 and MidLantic E170s to name a few), it's not that bad of a place...Friday, the first COA 738 with winglets will arrive as well!
Cheers and maybe we'll meet out there some day