Sunpak 383 or Vivitar 283 are the best, affordable (about 100$ in CDN) most powerful all-around flashes you can find. You can use them both on camera hotshoe and off-camera with a cord. They have manual (full, 1/2; 1/4; etc) and auto modes (range-based: 0.6 to 4m; 1m to 19m; etc).
The Sunpak 383 has a guide number of 130 (in feet @ 100 ISO), uses 4 AA batteries (get some lithium ones for max usage), and has both a tilt (90degs) and a swivel head (180deg). You can literally bounce the flash behind you, which is very useful in tight cramped spaces (although you would need a flash meter to help with proper exposure). Vivitar 283 has a little less movements, I think.
The Sunpak is still manufactured; the Vivitar was recently discontinued, but I've heard that the production has been restarted. They're pretty much the last non-TTL flashes left, and they're a must if you don't want to spend useless money to use them on pre-TTL cameras.
When I'm taking pictures at an event, I use the Sunpak at 45deg, auto 0.6m-4.5m range, with a diffuser on my Spotmatic. 50mm lens set between f5.6 and f8, 400 ISO film, hyperfocus, and I can do pretty much everything I need.
There is a battery pack for the Sunpak as well, which gives you amazingly quick recharge times, but it's a bit hard to come by. B&H sells it in the USA, I haven't seen it in Canada. No idea about continental Europe.