Condoms: Condoms are not freely available in all bars, let alone all sex bars and dark-rooms. Some bars have condoms and lube freely available, some sell condoms (but no lube) for about 50c a pop behind the bar, sometimes the barman will grudgingly give you one or two. Sometimes you have to bring your own.
A good place to get condoms and lube is in Mann-o-meter. Condoms are .25€ each or about 20€ for 100. Lube .35€ per sachet. Mann-o-meter is a voluntary organization which does HIV conselling and other stuff = "Berlins Gay and Lesbian Switchboard". It's in Nollendorfplatz on the corner of Bulow Strasse and Else-Lasker-Schuler Strasse. They are open daily 17.00 - 20.00.
Also just round the corner is Bruno's porn shop. The have shops at Nollendorfplatz/Bülowstr. 106 and Schönhauser Allee 131. As well as lavish supplies of porn they have reasonably priced condoms. Website at http://www.brunogmuender.com/.
A condom is a Kondom in German. Say it like English. But German's won't understand lube. They call it Gel here - pronounced with a hard g. Condoms and lube = Kondome und Gel.
Cruising: The main open air cruising is in Tiergarten. In the day there is sunbathing there as well as sex. A lot of the chaps are naked. Nakedness is considered quite natural in Germany. The Prussian park is another place.(TBR)
Rent: Rent boys gather on the corner of Fugger Strasse and Eisenacher Strasse. (see map) The rate is about 50€. HANG ON TO YOUR WALLET AND OTHER VALUABLES. Regard offers of free sex with extreme suspicion. Also expect disappointment. We investigated: Read here.
Darkrooms: Many bars and clubs in Berlin have darkrooms. It sort of goes without saying, and most of them have warning signs, don't take valuables in with you, pickpocketing is very common in darkrooms. If you have to, then keep your trousers done up!
Underwear / naked sex parties are frequent. You never have to carry money. You get a number, on a wrist band or written on your arm. They use the number to add up your bar bill and you pay before your leave. See Happy hours and sex parties for a quick list of them.