ok, this is edited post with new, confirmed and tested tables.

The base blocking animation numbers were provided by Ruvanal. Thanks.

The misleading tables were calculated by Galzohar. Thanks.

The new and much improved tables were calculated by Jurts, confirmed via testing by Ned_Devine and heavily scrutinized by Aurikan. Hail to you guys!

These are the tables then:

FBR A B C D
00% 3 4 5 6
05% 3 4 5 6
10% 3 4 5 6
15% 3 4 5 6
20% 3 4 5 5
25% 3 3 4 5
30% 3 3 4 5
35% 2 3 4 5
40% 2 3 4 4
45% 2 3 4 4
50% 2 3 3 4
55% 2 3 3 4
60% 2 3 3 4
65% 2 3 3 4
70% 2 2 3 4
75% 2 2 3 3

A - Pal/Am/Asn
B - Barb
C - Sorc/WB/WW
D - DruHuman/Nec

FBR:= SUM (all FBR items)

FBR from items (thanks to Flick for this list):

15% faster block rate: "of Blocking" suffix (or various set/unique shields)
20% faster block rate: Shael rune in shield
30% faster block rate: "of Deflecting" suffix (or various set/unique shields)

Certain unique/set shields have non standard blocking values:
Stormchaser (unique Scutum): 10%
Steelclash (unique Kite Shield): 20%
Radamant's Sphere (unique Ancient Shield): 20%
Stormshield (unique Monarch): 35%
Pelta Lunata (unique Buckler): 40%
Rhyme rune word shield: 40%
Whitstan's Guard (set Round Shield): 40%
Blackoak Shield (unique Luna): 50%
Griswold's Honor (set Vortex Shield): 65%

The only non-shield item that increases block rate is:
30% faster block rate: Guardian Angel unique Templar Coat

P.S. All shields have the same base block speed. Thanks to Karon and Ruvanal for nailing that...