If you are looking for a bar with no frills to spend the night, these are the best spots.
Memorie's Café is busy also, but there are a few working girls among the clients, making the atmosphere more trashy.
If you are ready to spend a few extra rupiah, you could try those restaurants, still walking distance: Tiga Nyonya (for traditional Indo-Chinese cuisine), Abuba Steak (best-value steaks in Jakarta), Beirut Lebanon (Lebanese food), Samarra (awesome setting but average middle eastern food), Ya-Udah Bistro (German food, but the quality decreased recently) or Garuda (open 24h).
You can find more information about Jakarta on these blog posts: Preparing a Weekend in Jakarta and Jakarta Nightlife Guide.
It has live music too and quite many tourists so it is easy to meet someone there if you are alone.
If you need AC, Absolute Café is another favourite of Jalan Jaksa nightlife, but most of its customers are regulars: English teachers, journalists, etc..
And now he was going to visit his homeland and Thailand as well. Since November the place was fully booked until very recently and the prospects look good as well.
It's an experience, but you'll probably die of boredom after 10 minutes.