Prices for 3G modems without contract have dropped significantly in Germany in 2009. Especially those from Vodafone are very cheap. Allthough they are unlocked, the dashboard in German Vodafone sticks won't work on other networks than Vodafone's. So if you want to use a Vodafone modem on another network you either need to download an open dashboard software or replace the installation files in the flashmemory of your Vodafone modem (= so-called "debranding"), so there will always be an open dashboard on your modem.
Note, that Vodafone modems in other countries come with real SIM- or netlocks and so can't be used on other networks after a debranding.

Vodafone USB modems are unlocked and come with a prepaid Vodafone WebSessions SIM.

Vodafone K3565-H

(Huawei E160X)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 900, 2100

pros:

• cheap
• easy debranding by simple update
• antenna connector underneath housing

contras:

• only 3,6 MBit/s downlink
• no HSUPA support
• no voice-call functionality

offers

• from ~€ 25 incl. shipping at eBay.de watch out for "K3565-H" or "Huawei" in description, since there's also the K3565-Z from ZTE, which can't be debranded that easy.
• € 29,50 incl. shipping at deltatecc (accepts PayPal and ships to Western Europe for € 15)
• € 29,90 at The Phone House shops (shop finder at bottom of this page), stock varies! may sell other models (Huawei E169, K3715 or E172 for the same price!)
• € 29,90 at MediaMarkt
• € 32,90 incl. shipping from logitel

Vodafone K3565-Z

(produced by ZTE)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 900, 2100

pros:

• cheap

contras:

• only 3,6 MBit/s downlink
• complicated debranding
• ZTE dashboard software inferior to Huawei's "Mobile Partner"
• no HSUPA support
• no antenna connector
• voice-call functionality - but currently no dashboard is using it

offers

• from ~€ 19 incl. shipping at eBay.de watch out for "K3565-Z" or "ZTE" in description, since there's also the K3565-H from Huawei
• € 29,90 at Vodafone shops

Vodafone K3520

(Huawei E169)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 900, 2100

pros:

• 7.2 MBit/s downlink
• easy debranding by simple update
• voice-call functionality
• antenna connector (underneath housing)

contras:

• no HSUPA support

offers

• € 29,90 at The Phone House shops (shop finder at bottom of this page), stock varies! may sell other models (Huawei E160X, K3715 or E172 for the same price!)
• from ~€ 40 incl. shipping at eBay.de
• € 42 incl. shipping from Handybund.de (offered on a German forum)

Vodafone K3715

(Huawei K3715, similar to Huawei E230)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 900, 2100

pros:

• 7.2 MBit/s downlink
• 1,45 MBit/s uplink
• easy debranding by simple update
• voice-call functionaliy

contras:

• no antenna connector

offers

• € 29,90 at The Phone House shops (shop finder at bottom of this page), stock varies! may sell other models (Huawei E160X, K3715 or E172 for the same price!)
• from ~€ 60 incl. shipping at eBay.de

Vodafone E172

(Huawei E172)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 850, 1900, 2100

pros:

• 7.2 MBit/s downlink
• 1,45 MBit/s uplink
• easy debranding by simple update

contras:

• no antenna connector
• no voice-call functionality

offers

• € 29,90 at The Phone House shops (shop finder at bottom of this page), stock varies! may sell other models (Huawei E160X, K3715 or E172 for the same price!)
• from ~70 incl. shipping at eBay.de

T-Mobile Web'n'Walk Stick IV
(Huawei E176)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 850, 1900, 2100

pros:

• 7.2 MBit/s downlink
• 5,76 MBit/s uplink
• easy debranding by simple update
• accessible antenna connector

contras:

• no voice-call functionality

offers

• € 59,90 at Penny supermarkets
• from ~€ 70 incl. shipping at eBay.de

Aldi MEDIONmobile WEB STICK S4011
(Huawei E160)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 850, 1900, 2100

pros:

• available at Aldi supermarkets
• easy debranding by simple update
• accessible antenna connector

contras:

• only 3,6 MBit/s downlink
• no HSUPA support
• no voice-call functionality

offers

• € 59,99 at Aldi supermarkets

Tchibo Internet Stick
(Huawei E160)

frequency bands:

GSM 850, 900, 1800, 1900
UMTS 850, 1900, 2100

pros:

• available in local Tchibo shops (more than 1000 throughout Germany)
• includes Tchibo SIM with attractive data tariffs
• easy debranding by simple update
• accessible antenna connector

contras:

• netlocked
• only 3,6 MBit/s downlink
• no HSUPA support
• no voice-call functionality

offers

• € 49,95 in local Tchbio shops and online