Do professors in Germany have other payment than their standard salary?
As Dirk writes, W3 only gives the Grundgehalt (base salary), which varies by state. As a public servant, you will automatically get a few hundred EUR on top if you are married and/or have children (Familienzuschlag). Note also that in some states (Bayern, Hessen, Sachsen), your W2 or W3 Grundgehalt will currently increase in two steps after 5/12 or after 7/14 years.

You can supplement the Grundgehalt with various Zulagen. These are pay increases, not one-time bonuses. You can get Zulagen either for a set period (befristete Zulage, i.e., a temporary one), or for the rest of your working life (unbefristete Zulage).


You can negotiate so-called Leistungszulagen (a performance bonus), for instance if you manage to get lots of third-party money, publish a lot, or supervise a lot of dissertations, or similar things. You typically discuss multi-year targets with your dean and/or university president or chancellor.
Some German states (Brandenburg, Bremen, Hamburg) currently give you a non-trivial Grundleistungszulage without any preconditions.
You may get Funktionszulagen if you hold particular offices, like being the dean or managing a larger group, or managing a specific institution or institute.
If you get an offer from a different university, you will start haggling with both the new university and the one you are at. Both usually want you, so both will offer you a Berufungszulage (a "job offer pay increase", at the university that extended the offer), or a Bleibezulage (a "staying pay increase", at the university that tries to keep you). In contrast to industry, this kind of haggling is normal. (In industry, if you get an outside offer but stay in exchange for a higher salary, your manager will usually assume that you won't stay much longer.)


As a brand-new professor, you may be able to get a small initial Berufungszulage, but most other Zulagen will only be negotiatable after a few years.

The Deutscher Hochschulverband is a good place to look for additional information. This is basically a union for professors and almost-professors in Germany, and they offer coaching to their members. Very much recommended in your first (and subsequent) salary negotiations - they know what you can reasonably demand and what not. A membership is definitely worth the dues. They also publish the pay scales currently here, in German, although this link will likely rot over time. 

In addition, you can get additional money from outside sources:


You can have consulting contracts in industry. You will usually need to clear this with your university, and your outside commitments will likely be capped at 8 hours per week or similar, but this can of course still mean serious money.
If you are a professor at a medical school or a Universitätsklinik, you will be able to see private patients and take home some of their payments, although this has been getting less lucrative in recent years, with the clinic keeping a larger cut from younger professors. You could set up your own practice on the side, but this would again be subject to limitations set by your employer.
As Wrzlprmft notes, you can get a little money out of the Verwertungsgesellschaft Wort, or VG Wort - see some information in English here. It essentially disburses monies as payments for people using your copyrighted works (they get their money from various sources). It's a very German institution. This will usually not be a lot of money, especially if you publish with a lot of coauthors. Here is what Academia.SE knows of VG Wort.
However, if you do publish a book, you will be able to keep any payments from the publisher. This will again usually not be a lot, and it's not specific to Germany.




Finally, note that a professor in Germany is a Beamter (public servant). This means that you pay far less in social security contributions, since you by definition can't lose your job (so no joblessness insurance contributions), and the state will pay your pension (so you don't need to contribute - although saving for your old age is still a good idea). The state also pays for part of your medical bills and those of your dependents (Beihilfe), and since you are a good risk (see above on not losing your job), you will get good deals on remaining health and other insurance policies. Bottom line: out of 75k EUR, you will take home a larger fraction than if you earned the same amount in industry.