How many interstates have you driven on?

[DandyDan]

I-24
I-29 (also have I-129, I-229 (MO) and I-229 (SD)
I-35 (also I-35E and I-35W in Minnesota, plus I-235, I-435, and I-635)
I-39
I-43
I-55 (also I-155, I-255 and I-355 in Illinois)
I-57
I-64
I-65 (also I-465 in Indiana)
I-66
I-69
I-70 (also I-470 (KS), I-470 (MO), I-670 (KS-MO), I-270 (MO-IL))
I-71
I-74 (also I-474 in Illinois)
I-75 (also I-475 in Ohio and I-275 in Michigan)
I-77
I-80 (also I-180 (NE), I-180 (IL), I-280 (IA-IL), I-380 (IA), I-480 (IA-NE), I-680 (IA-NE)
I-88 (W)
I-90 (also I-190 and I-290 in Illinois and I-490 in Ohio)
I-94 (also I-394, I-494 and I-694 in Minnesota, I-794 and I-894 in Wisconsin and I-294 in Illinois)
I-95 (also I-495 in VA and MD and I-395 in MD)

I may also have I-72, which I somehow didn't get my one time in Springfield, because I was in Jacksonville, IL, but I don't specifically remember my route that I followed when I was there (essentially following US 67). 

[elsmere241]

5: OR, WA
15: AZ, MT, NV, UT
24: TN
25: WY
26: NC
29: IA, MO, NE, SD
35: MO
40: NC, TN
55: IL
57: IL
64: VA
65: TN
66: VA
68: MD, WV
70: IN, OH, MD, MO, PA, UT, WV
72: IL
74: IL, IN
75: TN and possibly OH
76: NJ, OH, PA
77: NC
78: NJ, NY
79: PA, WV
80: CA, IA, NE, NV, UT, WY
81: PA, NY
82: OR, WA
83: MD and possibly PA
84: OR, UT
85: NC, SC, VA
90: ID, MT, NY, PA, SD, WA, WY
95: DC, DE, MD, NC, NJ, NY, PA, VA

Several 3dis as well, and maybe a few short 2di multiplexes.

[1995hoo]

I-4
I-10 (I-110 MS, I-110 FL, I-910 LA although it wasn't an Interstate then)
I-12 (I-140, I-240, I-440, I-540 all in NC)
I-24
I-26 (I-526 SC)
I-40
I-59 (I-459 AL)
I-64 (I-264 VA, I-664 VA)
I-65
I-66
I-68
I-70 (I-270 and its spur MD, I-270 OH, I-270 CO, I-370 MD, I-470 WV/OH)
I-71
I-73 (NC)
I-74 (NC)
I-75 (I-275 FL)
I-76 (eastern) (I-276, I-376, I-476 all in PA, I-676 PA/NJ)
I-77 (I-277 NC)
I-78 (I-278 NY/NJ)
I-79 (I-279 PA)
I-80 (I-280 NJ)
I-81 (I-581 VA)
I-83 (I-283 PA)
I-84 (eastern)
I-85
I-87 (I-287 NY)
I-90
I-91
I-95 (I-195 VA, I-195 MD, I-195 NJ, I-295 FL, I-295 MD/DC, I-295 DE/NJ, I-295 NY, I-295 ME, I-395 FL, I-395 VA/DC, I-395 MD, I-495 VA/DC/MD, I-495 DE, I-495 NY, I-495 MA, I-595 MD, I-695 DC, I-695 MD, I-695 NY, I-795 NC although it was not an Interstate then, I-895 and its spurs MD)
I-97

[NWI_Irish96]

Still missing quite a few, but the ones I have driven on:

10, 20, 24, 30, 40, 44, 64, 66, 70, 74, 76W, 78, 80, 88W, 90, 94, 96
5, 15, 19, 25, 35, 39, 43, 55, 57, 59, 65, 69, 71, 75, 77, 81, 95

205(CA), 310(LA), 225(CO), 635(TX), 238(CA), 355(IL), 164(IN), 264(KY), 265(IN), 265(KY), 465(IN), 865(IN), 469(IN), 270(CO), 270(IL/MO), 270(MD), 275(IN/KY/OH), 280(IA/IL), 580(CA), 880(CA), 285(GA), 190(IL), 290(IL), 194(MI), 294(IL), 794(WI), 894(WI), 195(MD), 295(DE/NJ), 295(DC/MD), 395(DC/VA), 495(DC/MD/VA), 695(DC), 196(MI), 296(MI), 496(MI), 696(MI)

[PHLBOS]

I'll list by state (DC = territory), c = clinched per state/territory

CT
I-84 c
I-91
I-95 c
I-291 c
I-395 c
I-684 c
I-691 c

DC
I-295 c

DE
I-95 c
I-295 c
I-495 c

GA (passenger only)
I-75
I-85
I-285

MA
I-84 c
I-90 c
I-91
I-93 c
I-95 c
I-190 c
I-195 c
I-290 c
I-291 c
I-295 c
I-395 c
I-495 c

MD
I-68 c
I-70
I-81 c
I-83
I-95 c
I-195 c
I-295 c
I-395 c
I-495 c
I-695

ME
I-95
I-295
I-395

NH
I-89
I-93
I-95 c
I-293
I-393 c

NJ
I-76 c
I-78
I-80
I-95 c
I-195
I-278
I-280
I-287 c
I-295 c
I-676 c

NY
I-84
I-86
I-87
I-90
I-95 c (as a passenger)
I-278
I-287 c
I-495
I-678
I-684 c

OH
I-76/80/90 (Ohio Turnpike sections)
I-80
I-75
I-280
I-475

OR
I-5
I-84 (as a passenger)
I-205 c
I-405 (as a passenger)

PA
I-70
I-76 c
I-78 c
I-79
I-80
I-81
I-83 c
I-95 c
I-99
I-176
I-276 c
I-279-north of I-376
I-376-section that was still signed as I-279 & PA 60 at the time
I-476
I-676 c

TN
I-24 (as a passenger)
I-40
I-65 (as a passenger)
I-75
I-81 c

TX
I-20
I-30
I-35E

VA
I-64
I-66
I-77
I-81 c
I-95
I-264
I-395
I-495 c

VT
I-89
I-91

WA
I-5
I-405 c

WV
I-68 c
I-79
I-81 c

[bassoon1986]

Clinched sections in bold

I-4
I-10 (TX, LA, MS, AL, FL
       I-110 (LA, FL, MS
       I-210 (LA)
       I-310 (LA)
       I-410 (TX)
       I-510 (LA)
       I-610 (LA, TX)
       I-910 (LA)
I-12
I-20 (TX, LA, MS, AL, GA)
       I-220 (LA, MS)
       I-820 (TX)
I-22
I-24 (TN,GA)
I-25 (CO, NM)
I-30 (TX, AR)
        I-130 (AR)
        I-430 (AR)
        I-530 (AR)
        I-630 (AR)
I-35 (TX, OK)
I-35E (TX)
I-35W (TX)
          I-635 (TX)
I-37
I-40 (NM, TX, AR, TN)
        I-240 (TN)
        I-440 (AR)
        I-540 (AR)
I-44 (MO, TX)
I-45
        I-345 (TX)
I-49 (LA)
I-55 (LA, MS, TN, AR, MO)
       I-155 (MO/TN)
       I-255 (MO/IL)
I-59 (MS, AL, GA)
        I-459 (AL)
I-64 (MO, KY, WV, VA)
I-65 (AL, TN, KY)
        I-265 (TN), (KY)
I-66 (VA)
I-69 (TX)
I-69E
I-70 (MO)
       I-170 (MO)
       I-270 (MO)
I-71 (KY, OH)
I-75 (FL, GA, TN, KY, OH)
I-77 (VA)
I-81 (TN, VA)
I-85 (GA)
       I-185 (GA)
I-89 (VT)
       I-189 (VT)
I-95 (VA)
       I-295 (VA)
       I-395 (DC, VA)
           

so I've been on 31 different 2di's, and 32 different 3di's, one being decomissioned since I've been on it (I-265 in Nashville)