Lake Maynara is a short drive west from Arusha - depending upon when you arrive in Tanzania this may be your first night's stop before heading on to Ngorongoro Crater and the Serengeti. There's another nearby park, Tarangire, that you may stop at depending upon the time of the year and animal migrations. Lake Maynara is famous for it's Tree Lions - although given that we didn't see any Lions in trees I wonder if this is more African Folk Stories than facts. Either way a drive through Lake Maynara includes lots of monkeys, zebras, deer, and giraffes.
When we were driving through the park a troop of monkeys were passing through on there way back home - I have no idea where they were coming from but it seemed like a fairly organized march.
We also saw the infamous blue ball monkey - I think that's its scientific name - a couple of times in this park.