The fan on my ti4200 failed; I replaced that card with a 9800 Pro.
The fan on my 9800 Pro failed; I put an aftermarket cooler on that card.
The fan on the aftermarket cooler started going out, but by that time I upgraded to a 6800 Ultra (it was actually a 6800 GS, but was factory overclocked and I was able to unlock the extra 4 pipelines, which made it identical in shaders and speed to a 6800 Ultra).
The 6800 GS I bought was from eVGA, and that fan never had a hiccup. When I built the new computer, I went with an 8800GT from eVGA, also factory overclocked. I'd say I haven't had a problem with it either, but it's only 4 months old right now.