Oh boy, I'm full of suggestions! You've come to the right person!
Considering that you're going for the grindy, over driven sound, I'd recommend the Mesa Bass 400+. It's all tubes and loud as a mother, reminicient of the old 70s SVTs (the new ones are good, but don't compare). The amp is a real plug-n-play type amp... you don't have to tweak your settings too much.
Sticking with all tube amps, you could also shoot for an Ampeg SVT. Like I mentioned before, the old 70s SVT's are the best, but the SVT-CL and SVT-II Pro are pretty good too. The only problem with these Ampegs is that they're really heavy (80 lbs for the amp alone). I would urge you to stay away from the SVT-3 Pro because it just doesn't have enough power to cut it.
If you don't mind tweaking the knobs and buttons on your amp, I'd recommend the Mesa M-2000 (my amp). It has 2 channels built in: tube and solid state, with a solid state power amp. It's got plenty of power (625 watts @ 4 ohms) and is much lighter than the rest of the amps I mentioned. It's greatest strength is also it's greatest weakness: the flexibility. The good thing is that you can dial in just about any sound on this. You can use the tube section by itself, the solid state section by itself, or blend the two. Plus you have 9 band EQs on each of the channels that can be set to on, off, or mix. Each channel has it's own compressor (which are actually really good!) with 3 settings (off, 3:1, 5:1) as well control of the frequencies affected and the threshold. The possibilities are virtually endless. The bad thing is that there are so many damn knobs and switches on here, that it's almost intimidating, and if you don't know what you're doing, it can make finding a good sound a real pain in the ass. (Having a good bass helps here too.) I know of people who haven't been able to do much with the amp because they couldn't handle it, but I myself love it. I play an Ibanez BTB 406, which is a pretty nice bass, and I like to get a really bass heavy (this amp has TONS of low end!), aggressive, gritty sound. With this amp, I've gotten just that, and I'm loving it. For more info, check out the mesa webpage:
http://www.mesaboogie.com
So yeah, that's my take on amps. I'm personally very fond of Mesa so I heartily recommend them. If you have any questions, let me know. I'm more than willing to help out a fellow bass player.
