bilboburgler

Generally you will find getting into a Rioja winery for a tasting a fair bit easier than a Ribera one if you just turn up on the day. Ribera tries to set itself a bit apart and there are guided tours (for $$) from Madrid there. Rioja is a bit more laid back and will let more just pop in, I'd start with the tourist website for Haro. The wiki link is also a good place to start http://en.wikipedia.org/wiki/La_Rioja_%28Spain%29

I suggest that you can taste Sherry all over Spain and while looking at a Sherry solera is, well like looking at a load of barrels, tasting it with black foot ham in a bar is a moment for "Trumpets and Lamprey". I have found visiting Jerez is ok but even for a wine "expert" I find the experience poor in comparison to other visits, if you have never understood the whole sherry concept then there is nowhere else I would prefer to learn it. Still if you are in Cordoba try and get some innocent City of Cadiz white (palomino grape) to go with fish (very pleasant combination).

CathyM

In my personal experience visiting La Rioja I haven't found it easy to just show up for a visit without an appointment. I've found quite the opposite with visits for wineries often full far in advance. For example, on my last trip I tried to book 2 separate places in July for a visit in September to Haro and the dates were already full. The only exceptions I've found are the 2 bodegas in Laguardia that offer the cave tours - but these are not exactly the large bodegas and the wine not ver good. It's more for the experience of visiting the underground caves. With only 2 days for La Rioja I wouldn't suggest showing up without reservations or the OP may end up not even getting to visit a bodega.

As for Andalucia, another idea would be to take a few days and stay in Cadiz. From Cadiz you could visit Arcos, Vejer, Medina Sidona and for sherry tasting Jerez, El Puerto and Sanlucar. All of these places are well accessed by public transportation. Another reason to drop the Rioja/Ribera del Duero from this trip....