Staying in Brighton this weekend. Any recommendations for where to ride?
Stanmer park (singletrack) and Wild Park (some berms jumps etc)
South Downs way might be your best bet, being at the top of the hills it drys more quickly. Brighton to Eastbourne will make a good ride and you can take a diversion to Friston Forest though I expect that'll be pretty muddy. If you don't fancy the ride back its easy to get the train back to Brighton from Eastbourne.
you could try the brightonmtb.org site too.
all a bit of a mudfest at the moment though so you might be better trying to stay 'up top' and doign the xc thing.
On top of what's already been mentioned if it's lairy descents you're after there's a couple of options on Devils Dyke just outside Brighton that can be fun. Flat out down the middle will get you well over 50mph or there's a more demanding singletrack down the side.
Out East towards Offham there's Blackcap hill which has a farm track that starts from the gate where the South Downs way turns south away from the main ridgeline. It's steep and packed with several jumps formed from where they build large humps across it to divert water away. Again you can easily get over 40mph down there and some big air in the process. This is my favourite descent near to home and being fairly straight/open you can safely reach these speeds whilst being able to see far enough ahead to be able to stop should you need to.
Aside from that, any descent down the north facing, scarp slope of the downs can be fun. It's pretty steep in places.
Stanmer park is king for singletrack, and you can park at the sussex uni for free at the weekends (as long as there isn't a football match)It's not too hidden but your best bet would be to find and follow someone to make the most of it.
The Wildpark next to stammer park is your best bet for short DH runs, plenty of berms and small jumps concentrated into a few min run should put a smile on your face.
In the same ride you can also easily hit the south downs, very open and long shallow climbs to clock up some miles.
As avdave said, on the top of the downs will be driest, Friston Forest was very wet and muddy in most places last weekend, some tree covered areas drain pretty well but the weather as been very challenging to so the least. Tempted to get a road bike.
If you can, stay away from Stanmer - most of the trails really suffer if ridden in their current condition.