For scanner support there is the package SANE (Scanner Access Now Easy). Information can be found at here. It can be downloaded from here. This is a universal scanner interface. It comes complete with documentation and several frontends and backends.
More information on handheld scanners can be found at here
Many scanners also have their own, scanner specific, software packages which include drivers.
A4 Tech AC 4096 / AS 8000P (a4scan) here
Conrad Personal Scanner 64, P105 handheld scanners (scan-driver) here
Epson GT-5500 (SANE epson)
Epson GT-6000 here
Escom Image Scanner 256 (SANE umax)
Fujitsu SCSI-2 scanners contact Dr. G.W. Wettstein < greg%wind.UUCP@plains.nodak.edu>
Genius GS-B105G handheld scanner (gs105) here
Genius GeniScan GS-4500, GS-4500A handheld scanners (gs4500) here
HighScreen Greyscan 256 handheld scanner (BW only) (gs4500) here
HP ScanJet II series SCSI here
HP ScanJet IIc, IIcx, IIp, 3c, 4c, 4p, 5p, 5pse, plus here
Linotype Hell Jade, Jade2 (SANE umax)
Logitech Scanman+, Scanman 32, Scanman 256 handheld scanners (logiscan) here
Microtek ScanMaker E3, E6, II, IIXE, III and 35t models ??? here ??? here E3 and E6 scanners are also supported by here
Mustek M105 handheld scanner (scan-driver) here
Mustek HT800 Turbo, Matador 105, Matador 256 handheld scanners (scan-driver) here
Mustek Paragon 6000CX here
Nikon Coolscan SCSI 35mm film scanner here
Nikon AX-210 (SANE umax)
Pearl 256 handheld scanner (scan-driver) here
Polaroid DMC (SANE dmc)
Vobis/Highscreen Scanboostar Premium (SANE umax)
UMAX SCSI scanners here
UMAX Vista S6, S6E, T630, Supervista S-12 (SANE umax)
UMAX S-6E, S-6EG, S-12, S-12G (SANE umax)
UMAX Astra 600S, 610S, 1200S, 1220S (SANE umax)
UMAX UC 630, 840, 1200S, 1200SE (SANE umax)
UMAX UG 80, 630 (SANE umax)
UMAX PSD, Gemini D-16 (SANE umax)
NOTE: The Mustek drivers work only with GI1904 interface cards. Eric Chang eric.chang@chrysalis.org has created a patch to use them with IF960 interface cards.
Abaton Scan 300/S (SANE abaton)
Abaton Scan 300/GS (SANE abaton)
Agfa Focus, Focus II (SANE agfafocus)
Agfa Focus Color, Focus Color Plus (SANE agfafocus)
Agfa Focus Lineart (SANE agfafocus)
Agfa Arcus II (SANE microtek)
Agfa StudioScan II, IIsi (SANE microtek)
Agfa SnapScan 300, 310, 600 (SANE snapscan)
Apple Scanner, OneScanner, ColorOneScanner (SANE apple)
Artec/Ultima AT3, AT6, AT12 (SANE artec)
Artec A6000C+ (SANE artec)
Canon CanoScan 300, CanoScan 600, CanoScan 2700F (SANE canon)
Genius Colorpage-Vivid+ Info can be found on here. The driver can also be found here.
Genius GS-4000, ScanMate/32, ScanMate/GS handheld scanners (gs4500) here
HP ScanJet IIc, IIp, IIcx, 3c, 4c, 3p, 4p, 5p, 6100c, 6200c (SANE hp)
HP PhotoSmart PhotoScanner (SANE hp)
Kodak DC210 (SANE dc210)
Kodak DC20, DC25 (SANE dc25)
Microtek Scanmaker E2, E3, E6, II, IIG, IIHR, IISP, III, 35t+, 600Z(S), 600G(S) (SANE microtek)
Microtek ScanMaker E3plus, 330, 630, 636, X6 (SANE microtek2)
Microtek Phantom 636 (SANE microtek2)
Mustek MFC-600S, MFC-600CD, MFC-800S (SANE mustek)
Mustek MFS-6000CX, MFS-6000SP, MFS-8000SP, MFS-1200SP, MFS-12000CX (SANE mustek)
Mustek SE-6000SP, SE-12000SP (SANE mustek)
Mustek HT105, M800 handheld scanners (scan-driver) here
Nework Scanny MM100 Info can be found on here. The driver can also be found here.
Nikon LS-20, LS-30, LS-1000 (SANE Coolscan)
Plustek OpticPro 4830P, OpticPro 4831P, OpticPro 9630P/PL, OpticPro 600P, OpticPro FBIII, OpticPro FBIV (SANE plustek) The sane driver can be found at here
Primax Colorado Direct 300, Colorado Direct 600/30bit, Storm Totalscan Info can be found on here. The driver can also be found here.
Siemens S9036 (SANE agfafocus)
Tamarack Artiscan 6000C, 8000C, 12000C (SANE tamarack)
UMAX Vista-S8, UC-1260, Mirage IIse, PL-II (SANE umax)
Vobis HighScan (SANE microtek2)
Voelkner Personal Scanner 64 handheld scanner (scan-driver) here
Vuego 310S (SANE snapscan)
Acer scanners. Acer is not releasing any programming information.
Escom 256 (Primax Lector Premier 256) handheld scanner
Genius ScanMate/256, ScanMate/Color, EasyScan handheld scanners
Mustek CG 8000 handheld scanner
Primax Colorado Direct 9600, Colorado 1200p, Colorado USB 19200 Info can be found on here
Trust Ami Scan handheld scanner
UMAX parallel scanners