Here is a comprehensive list of most user agents that you may come across in your website log. Don't know how, but it may come in handy to someone.
A
User Agent Name ------ Deployed by
Acoon Robot v1.01 (www.acoon.de) Acoon
AltaVista Intranet V1.0 AltaVista Search Intranet PX V1.0
webmaster@messebasel.ch Messe Basel
AltaVista Intranet V1.0 bluewindow.ch
webmaster@bluewin.ch sear.ch
AltaVista Intranet V1.0 pta.at
webmaster@pta.at search.at
AltaVista Intranet V1.0 Re-Index
webmaster@bluewin.ch sear.ch
AltaVista Intranet V2.0 pta.at
webmaster@pta.at search.at
AltaVista Intranet V2.0 Sear.ch
ccc@bluewin.ch sear.ch
AltaVista Intranet V2.0
www.altavista.de search-support@altavista.de AltaVista Deutschland
AnzwersCrawl/2.0 (anzwerscrawl@anzwers.com.au; [http://faq.anzwers.com.au/anzwerscrawl.html)] Anzwers
Arachnoidea (arachnoidea@euroseek.com) EuroSeek
ArchitextSpider Excite
C
User Agent Name ------ Deployed by
CherryPickerSE/1.0 CherryPicker
CherryPickerElite/1.0 CherryPicker
Crescent Internet ToolPak HTTP OLE Control v.1.0 ExtractorPro
Crescent Internet ToolPak HTTP OLE Control v.1.0 WebWeasel
Crescent Internet ToolPak HTTP OLE Control v.1.0 Web Mole
E
User Agent Name ------ Deployed by
EmailCollector/1.0 EmailCollector
EmailSiphon EmailSiphon
EmailWolf 1.00 emailWolf
Enfish Tracker Enfish
ExtractorPro ExtractorPro
F
User Agent Name ------ Deployed by
fido/1.0 Harvest/1.4.pl2 PlanetSearch
G
User Agent Name ------ Deployed by
GAIS Robot/1.0B2 seednet
Googlebot/1.0 (googlebot@googlebot.com [http://googlebot.com/)] Google
Gulliver/1.2 Northern Light
I
User Agent Name ------ Deployed by
ia_archive (NewsFetcher 1.0) (http://www.alexa.com/
crawler@alexa.com) Alexa
ia_archiver Alexa
ia_archiver/1.6 Alexa
Infoseek Sidewinder/0.9 Infoseek
J
User Agent Name ------ Deployed by
Java1.1.3 Bobby
K
User Agent Name ------ Deployed by
KGValidator/1.3 libwww-perl/0.40 KGValidator
KIT_Fireball/2.0 Fireball
L
User Agent Name ------ Deployed by
LECodeChecker/2.0 libwww/5.1f LinkExchange
libwww-perl/5.18 LinkExchange
lwp-trivial/1.27 Search 4 Free
Lycos_Spider_(T-Rex)/3.0 Lycos
M
User Agent Name ------ Deployed by
Mozilla/2.0 (compatible; EZResult -- Internet Search Engine) EZResult
Mozilla/2.0 (compatible; NEWT ActiveX; Win32) WebCollector
Mozilla/2.0 (compatible; T-H-U-N-D-E-R-S-T-O-N-E) Thunderstone
Mozilla/3.0 Gold (Win95; I) Web Site Garage
Mozilla/3.0 (compatible; MuscatFerret/1.4.1;
olly@muscat.co.uk) EuroFerret
Mozilla/3.0 (compatible; MuscatFerret/1.5.2;
olly@muscat.co.uk) EuroFerret
Mozilla/3.0 (compatible; MuscatFerret/1.5.3;
olly@muscat.co.uk) EuroFerret
Mozilla/3.01 (Win95; I) Infoseek
Mozilla/4.0 (compatible; MSIE 4.0; MSIECrawler; Windows 95) MSIE Crawler
Mozilla/4.04 [de] (Win95; I ;Kolibri gncwebbot) Kolibri Online
Mozilla/4.04 [de] (Win95; I ;Nav; Kolibri gncwebbot) Kolibri Online
N
User Agent Name ------ Deployed by
Namecrawler/1.0 NetNames
S
User Agent Name ------ Deployed by
Scooter/1.0 AltaVista
Scooter/1.0
scooter@pa.dec.com AltaVista
Scooter/1.1 (custom) AltaVista
Scooter/2.0 G.R.A.B. X2.0 AltaVista
Scooter/2.0 G.R.A.B. V1.1.0 AltaVista
search.at V1.2 search.at
sexsearcher Sexsearcher
Slurp/2.0 (slurp@inktomi.com; [http://www.inktomi.com/slurp.html)] Hotbot
Slurp.so/1.0 (slurp@inktomi.com; [http://www.inktomi.com/slurp.html)] Hotbot
Squid/1.1.19 Squid
SwissSearch V1.2 SwissSearch
T
User Agent Name ------ Deployed by
The Informant The Informant
U
User Agent Name ------ Deployed by
Ultraseek Infoseek
V
User Agent Name ------ Deployed by
ValueClick Robocop/0.2b ValueClick
W
User Agent Name ------ Deployed by
W3C_Validator/1.0 libwww-perl/0.40 W3C Validator
WebCrawler/3.0 Robot libwww/5.0a WebCrawler
WebCrawler-AddURL/2.0 WebCrawler
WiseWire WiseWire
WiseWire-Alpha-1.0 WiseWire
WiseWire-Alpha-Spider WiseWire
WiseWire-Alpha12-Spider971219a WiseWire
WiseWire-Alpha12-Spider(971223a) WiseWire
WiseWire-HotSpider-1.0 WiseWire
WiseWire-Spider WiseWire
WiseWire-Spider-1.0 WiseWire
WiseWire-Spider2 WiseWire
WiseWire-Widow-1.0 WiseWire
WiseWire-Widow-1.0r WiseWire
WiseWire-Widow-1.0-ALPHA12 WiseWire
Non-Alphanumerical / Empty Strings
User Agent Name ------ Deployed by
/0.5 libwww-perl/0.40 DoctorHTML
[empty] Email Magnet
[empty] eMailReaper
[empty] Lycos
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