Hi
We made the same trip (now we re going uo the east coast), starting in May 2011 and there where some big changes! We where always looking in forums, and surprised with so many "bad" news. (we hold portuguese EU passport).
Here are the major news
Burkina - doing it in the border costs now 150€ p person! It was 25€. If you do it in Bamako I heard it s half price
Gana - in Ouagadogo (Burkina) they only give us if we where residents in Burkina. New rules they said. We got it because I had a flight already bought (for 15 days working n Europe) from Accra, so I printed it, got a interview with their consul, and attached a verbal note from my Consul in Burkina.
Nigeria - It took us 15 days on Accra to do it, again with a verbal note from our embassie explainig our project
Congo DRC - we were there before elections so maybe it was a special time. It took us 15 days, and we only manage after our Embassedor in RDC gave directly a letter of invitation in the Foreing Affairs in Kinhasa. All the travellers we met there where refused.
Angola - They stop giving transit visas like before in Congo and Nigeria. Once again we were lucky, had our embassies helping a lot (in Angola e Congo) and the advantage of beijng portuguese with many friend in Angola. But it s the hardest visa in west Africa these days.
Probably many changed already! Crazy paperwork.
Usualy the best its to do it at home, or try is to get a letter from your embassie explainig what you re doing. We heard many embassies - english, japaneses, deutch, don t do it. On that we re lucky beijng from a small latin country!
Cheers
Carlos
Not 2 late trip (all visa stories detailed in "tips")