So this is a list of all the item definition indexes that I have found, the hat indexes were found by Damizean.
Usage: SetEntProp(edict, Prop_Send, "m_iItemDefinitionIndex", index);
Weapons:
0 - Scout's Bat
1 - Demoman's Bottle
2 - Pyro's Axe
3 - Sniper's Kukri
4 - Spy's Knife
5 - Heavy's Fists
6 - Soldier's Shovel
7 - Engineer's Wrench
8 - Medic's Bonesaw
9 - Enginner's Shotgun
10 - Soldier's Shotgun
11 - Heavy's Shotgun
12 - Pyro's Shotgun
13 - Scout's Scattergun
14 - Sniper's Rifle
15 - Heavy's Minigun
16 - Sniper's SMG
17 - Medics Syringegun
18 - Soldier's Rocket Launcher
19 - Demoman's Grenade Launcher
20 - Demoman's Sticky Bomb Launcher
21 - Pyro's Flamethrower
22 - Engineer's Pistol
23 - Scout's Pistol
24 - Spy's Pistol
25 - Engineer's Builder
26 - Engineer's Demolisher
27 - Spy's Disguise Kit
29 - Medic's Ubergun
30 - Spy's Watch
35 - Medic's Kritzkrieg
36 - Medic's Blutslauger
37 - Medic's Ubersaw
38 - Pyro's Axetinguisher
39 - Pyro's Flaregun
40 - Pyro's Backburner
41 - Heavy's Natascha
42 - Heavy's Sandvich
43 - Heavy's Killer Gloves Of Boxing
44 - Scout's Wooden Bat
45 - Scout's Force-A-Nature
56 - Sniper's Huntsman
57 - Sniper's Razorback
58 - Sniper's Jarate
59 - Spy's Dead Ringer
60 - Spy's Cloak And Dagger
61 - Spy's Ambassador
Hats:
47 - Demoman's 'Fro
48 - Mining Light
49 - Football Helmet
50 - Prussian Pikelhaude
51 - Pyro's Beanie
52 - Batter's Helmet
53 - Trophy hat
54 - Soldier's Stash
55 - Fancy Fedora
94 - Texas Ten Gallon
95 - Engineer's Cap
96 - Officer's Ushanka
97 - Tough Guy's Tuque
98 - Stainless Pot
99 - Tyrant's Helm
100 - Glengarry Bonnet
101 - Vintage Tyrolean
102 - Respectless Rubber Glove
103 - Camera Beard
104 - Otolaryngologist's Mirror
105 - Brigade Helm
106 - Bonk Helm
107 - Ye Olde Baker Boy
108 - Backbiter's Billycock
109 - Professional's Panama
110 - Master's Yellow Belt
120 - Scottsman's Stove Pipe
Apologies in advance for any typos or incorrect names, however you should be able to work out what each item is.